Clean up imports

[perimosocordiae]

• move (almost) all imports to the top of the file
• use the absolute_import syntax

This should help make any environment issues easier to debug, as missing imports will fail quickly.

[jsaponara]

Merged! The tests run fine but the linter sees errors. If you get a chance please let me know what you think the problem is. Thanks yet again CJ!

lint runtests: commands[0] | /home/john/dev/tax/opentaxforms/linting/fail-on-errs-only.sh
************* Module opentaxforms.Form
opentaxforms/Form.py:13: [E0401(import-error), ] Unable to import 'six.moves.urllib.request'
opentaxforms/Form.py:14: [E0401(import-error), ] Unable to import 'six.moves.urllib.error'
************* Module opentaxforms.config
opentaxforms/config.py:9: [E0401(import-error), ] Unable to import 'six.moves.urllib.request'
opentaxforms/config.py:10: [E0401(import-error), ] Unable to import 'six.moves.urllib.error'
************* Module opentaxforms.html
opentaxforms/html.py:81: [E0401(import-error), readImgSize] Unable to import 'PIL'
FAIL general linting: errors occurred

[perimosocordiae]

Seems like the linting environment doesn't have the appropriate packages installed.