Add Google calendar event handler

[chime3]

Closes #97

[chime3]

[tahpot]

Test isn't passing for me.

[chime3]

What's changed

• Replaced timestamp based item tracking with ID & pageToken tracking
• Modified common units for custom handler config
• Common unit tests cases are mainly checking basic item IDs

How to test

[chime3]

You can't make changes to tests/common.tests.ts. That is used by the other handler tests.

Reverted and didn't use runGenericTests function of common unit tests, but used buildTestObjects and checkItem function.

Instead, added test cases in calendar-event.tests.ts file.