Add support for Python3 and IDA 7.x

[nazywam]

Changelog:

• Migrated codebase to python3
• Migrated idaapi from 6.x to 7.x
• Removed wildcard imports in favour of explicit ones
• Added type hints for some functions
• Fixed codebase to be pep8-compliant
• Commented out unused variables (they can probably be safely deleted in a future refactor)

Flake8 output:

➜  ida_ifl git:(feature/python3) flake8 ifl.py --max-line-length=256                                                                                                                                                                                                              18:23:20
ifl.py:19:1: E402 module level import not at top of file
ifl.py:20:1: E402 module level import not at top of file
ifl.py:22:1: E402 module level import not at top of file
ifl.py:24:1: E402 module level import not at top of file
ifl.py:28:1: E402 module level import not at top of file
ifl.py:31:1: E402 module level import not at top of file
ifl.py:32:1: E402 module level import not at top of file
ifl.py:33:1: E402 module level import not at top of file
ifl.py:35:1: E402 module level import not at top of file

Mypy output (ran inside an IDA instance) - still not perfect:

Python>from mypy import api
Python>for p in api.run(["/home/michal/work/ida_ifl/ifl.py"]):
Python>     print(p)
Python>
/home/michal/work/ida_ifl/ifl.py:63: error: Need type annotation for 'local_variables'
/home/michal/work/ida_ifl/ifl.py:64: error: Need type annotation for 'arguments'
/home/michal/work/ida_ifl/ifl.py:365: error: Name 'g_DataManager' is not defined
/home/michal/work/ida_ifl/ifl.py:499: error: Need type annotation for 'refs_list'
/home/michal/work/ida_ifl/ifl.py:706: error: Need type annotation for '_importsSet'
/home/michal/work/ida_ifl/ifl.py:707: error: Need type annotation for '_importNamesSet'
/home/michal/work/ida_ifl/ifl.py:809: error: Need type annotation for '_functionsMap'
/home/michal/work/ida_ifl/ifl.py:810: error: Need type annotation for 'funcList'
/home/michal/work/ida_ifl/ifl.py:890: error: Cannot determine type of 'subDataManager'
/home/michal/work/ida_ifl/ifl.py:936: error: Cannot determine type of 'refs_label'
/home/michal/work/ida_ifl/ifl.py:950: error: Cannot determine type of 'refs_tabs'
/home/michal/work/ida_ifl/ifl.py:951: error: Cannot determine type of 'refs_tabs'
/home/michal/work/ida_ifl/ifl.py:957: error: Cannot determine type of 'addr_view'
/home/michal/work/ida_ifl/ifl.py:958: error: Cannot determine type of 'addr_view'
/home/michal/work/ida_ifl/ifl.py:959: error: Cannot determine type of 'addr_view'
/home/michal/work/ida_ifl/ifl.py:961: error: Cannot determine type of 'addr_view'
/home/michal/work/ida_ifl/ifl.py:962: error: Cannot determine type of 'addr_view'
/home/michal/work/ida_ifl/ifl.py:963: error: Cannot determine type of 'addr_view'
/home/michal/work/ida_ifl/ifl.py:972: error: Name 'g_DataManager' is not defined
/home/michal/work/ida_ifl/ifl.py:981: error: Cannot determine type of 'refs_view'
/home/michal/work/ida_ifl/ifl.py:981: error: Cannot determine type of 'refsto_model'
/home/michal/work/ida_ifl/ifl.py:982: error: Cannot determine type of 'refsfrom_view'
/home/michal/work/ida_ifl/ifl.py:982: error: Cannot determine type of 'refsfrom_model'
/home/michal/work/ida_ifl/ifl.py:992: error: Cannot determine type of 'criterium_id'
/home/michal/work/ida_ifl/ifl.py:994: error: Cannot determine type of 'addr_sorted_model'
/home/michal/work/ida_ifl/ifl.py:995: error: Cannot determine type of 'addr_sorted_model'
/home/michal/work/ida_ifl/ifl.py:1001: error: Cannot determine type of 'filter_combo'
/home/michal/work/ida_ifl/ifl.py:1001: error: Cannot determine type of 'filter_edit'
/home/michal/work/ida_ifl/ifl.py:1005: error: Cannot determine type of 'filter_edit'
/home/michal/work/ida_ifl/ifl.py:1006: error: Cannot determine type of 'is_livefilter'
/home/michal/work/ida_ifl/ifl.py:1014: error: Cannot determine type of 'criterium_combo'
/home/michal/work/ida_ifl/ifl.py:1016: error: Cannot determine type of 'filter_edit'
/home/michal/work/ida_ifl/ifl.py:1018: error: Cannot determine type of 'filter_edit'
/home/michal/work/ida_ifl/ifl.py:1022: error: Cannot determine type of 'livefilter_box'
/home/michal/work/ida_ifl/ifl.py:1024: error: Cannot determine type of 'filter_combo'
/home/michal/work/ida_ifl/ifl.py:1024: error: Cannot determine type of 'filter_edit'
/home/michal/work/ida_ifl/ifl.py:1046: error: Name 'g_DataManager' is not defined
/home/michal/work/ida_ifl/ifl.py:1087: error: Name 'g_DataManager' is not defined
/home/michal/work/ida_ifl/ifl.py:1246: error: Name 'g_DataManager' is not defined
/home/michal/work/ida_ifl/ifl.py:1248: error: Name 'g_DataManager' is not defined
/home/michal/work/ida_ifl/ifl.py:1251: error: Name 'm_functionInfoForm' is not defined
/home/michal/work/ida_ifl/ifl.py:1254: error: Name 'm_functionInfoForm' is not defined
/home/michal/work/ida_ifl/ifl.py:1256: error: Name 'm_functionInfoForm' is not defined

Test plan:
Try using the script on various compatible IDA versions.

Closes #9