Bug 940295 - Refactor test_calendar_new_event to use default date values. Also clean up calendar app locators

Conflicts:
	tests/python/gaia-ui-tests/gaiatest/tests/functional/calendar/manifest.ini
Merge pull request #14315 from AndreiH/bug_940295_v1.2

Bug 940295 - Refactor test_calendar_new_event to use default date values...