Exclude vesting events past a grant cancellation from the Vesting History

[franckc]

Fix for #14

• Added a new cancelled property on the vesting event object returned by the server.
• The UI now checks on that property when using events in the VestingHistory and VestingBar component
• Added unit tests for the new code. Tweaked some older unit tests to use UTC tz otherwise they were failing when ran on a host in Daylight saving time :)

Here is a couple of snapshot showing the old vs new behavior with a grant having a cancellation date of 2021-06-15

UI before (notice how it shows vesting events past the cancellation date):

UI after (notice how it dos not show vesting events past the cancellation date):

[shahthepro]

LGTM