Add calendarViewController to tabbar

[kindraywind]

What's in this PR:

• Refactored event getters from VCs to CalendarAPI for now.
• Added CalendarViewController to tabbar The picture speaks for itself

[codecov[bot]]

Codecov Report

Merging #15 into master will decrease coverage by 2.35%. The diff coverage is 45.09%.

@@            Coverage Diff             @@
##           master      #15      +/-   ##
==========================================
- Coverage    62.1%   59.75%   -2.36%     
==========================================
  Files          23       25       +2     
  Lines        1008     1133     +125     
  Branches       47       49       +2     
==========================================
+ Hits          626      677      +51     
- Misses        381      455      +74     
  Partials        1        1

Impacted Files	Coverage Δ
...alendar/Views/Cells/EventHeaderTableViewCell.swift	0% <0%> (ø)	:arrow_up:
...hEventsCalendarUITests/TabbarControllerTests.swift	100% <100%> (ø)
...endar/ViewControllers/EventTabViewController.swift	87.5% <50%> (+2.2%)	:arrow_up:
...endar/ViewControllers/CalendarViewController.swift	8.97% <8.97%> (ø)
ThaiTechEventsCalendar/Networks/CalendarAPI.swift	75% <81.25%> (+10.29%)	:arrow_up:
ThaiTechEventsCalendarTests/CalendarAPITests.swift	80% <82.35%> (ø)

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