Refactor Calendar Module

See merge request !9

Add more tests to the CLI subclasses

See merge request !7

Add tests to MainTest.java

See merge request !5

# Conflicts:
#   .gitlab-ci.yml

Merge current test progress to staging

See merge request !3

Add the ability for User to register, Admin to set coordinator role and see TA's calendar with permission

Make Project to Use Gradle

See merge request !2

# Conflicts:
#   README.md

Iteration 2

See merge request !1