Implement a check on ini files

[lra]

To prevent errors like:

Traceback (most recent call last):
  File "/usr/local/bin/mackup", line 11, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.6/site-packages/mackup/main.py", line 65, in main
    app_db = ApplicationsDatabase()
  File "/usr/local/lib/python3.6/site-packages/mackup/appsdb.py", line 34, in __init__
    if config.read(config_file):
  File "/usr/local/Cellar/python/3.6.4_4/Frameworks/Python.framework/Versions/3.6/lib/python3.6/configparser.py", line 697, in read
    self._read(fp, filename)
  File "/usr/local/Cellar/python/3.6.4_4/Frameworks/Python.framework/Versions/3.6/lib/python3.6/configparser.py", line 1092, in _read
    fpname, lineno)
configparser.DuplicateOptionError: While reading from '/usr/local/lib/python3.6/site-packages/mackup/applications/bettertouchtool.cfg' [line  9]: option 'Library/Application Support/BetterTouchTool/btt_data_store.v2' in section 'configuration_files' already exists