Code review comment for lp:~knightrider0xd/openlp/propresenter_5-6_import

I've implemented the requested changes, with the exceptions of refactoring the code for self.copyright and self.ccli_number.

While the code appears similar across all versions, it differs for version 6:
# ProPresenter 4 & 5
self.copyright = root.get('CCLICopyrightInfo')
self.ccli_number = root.get('CCLILicenseNumber')

# ProPresenter 6
self.copyright = root.get('CCLICopyrightYear')
self.ccli_number = root.get('CCLISongNumber')