Add specs for Holidays model.
Update factory for creating holidays with avatars.
Update holidays model for valitation presence of avatar. Update holidays_controller_spec for test creating new holiday with avatar. Update factory for using fixtures.
Refactoring: Update factory (delete duplication, replace double quotes with single).
Update holidays_controller_spec: added check that it is impossible to update the holiday with invalid avatar.
Refactoring: Update some files for new hash syntax.