New UI integration

[geofot96]

Implemented the new app UI using a bottom navigation bar as discussed in the previous sprint panning . This implementation comes with many changes as the activities we had so far (GroupsActivity, ProfileActivity, MergedCalendarActivity) have been replaced by fragments.

Notes

• MergedCalendarActivity has been placed in the tab just as a placeholder and can be replaced easily if necessary.
• The classes for GroupsActivity, ProfileActivity, MergedCalendarActivity are now empty and hence not necessary. I haven't deleted them yet to facilitate conflict resolution but will be deleted eventually.
• 4 existing tests fail and that's expected as they relied on the previous implementation. They are to be updated and more tests will be added before merging.
• The manifest will be modified as well so that NavigationActivity becomes the main activity. For now one can navigate to the new UI through the TABBAR button in the MainActivity.

[codeclimate[bot]]

Code Climate has analyzed commit 7f070876 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 87.1% (80% is the threshold).

This pull request will bring the total coverage in the repository to 84.7% (0.2% change).

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