Improve the add_vcal_file method

- When adding a meeting we need to if the user is an admin or not (the backend library
has no access to this information and thus rely on the frontend)
- Skip the VTIMEZONE when parsing an iCalendar file, we do nothing with them
- Don't fail in case the object has no summary
Fix the upload_calendar function

- Forward to the backend if the user is an admin or not
- Catch exception in case add_calendar throws one
- Ignore pieces of code we can't/don't test
Add sample ical files used to tests the upload
Declare the icalendar file and make the groups FakeUser empty by default
Add tests for the upload_calendar method in the UI and fix the add_calendar if there is no network
Lift the constraint to flask < 0.10 in requirements.txt

- The unit-tests benefits from having a recent version of flask
- python-fedora is now compatible with flask >= 0.10