[Timer] Re-implement Timer object in Vue.js

[khalidadil]

The existing Timer object is currently implemented as a legacy bundle and written in Angular.js. It should be re-implemented as a plugin under /src/plugins using our current API, with the UI migrated to Vue.

Any legacy code associated with the legacy Timer object should be removed from the code-base.

[khalidadil]

Testing instructions

Local Testing

If possible, create a timer in a branch before this change and then switch to the branch with the new timer. Ensure that the timer continues to display properly and that editing the properties works.

Other Testing

1. Create a timer object and choose some values in the creation dialog. Ensure that the timer is displayed and is in the appropriate format based on the options chosen (counting up/down and correct duration shown).
2. Edit the properties to modify the display format and ensure the timer updates with the correct format.
3. Try pausing the timer from the context menu and make sure the timer pauses.
4. Try stopping the timer from the context menu and make sure the timer stops and resets the display to --:--:--.
5. Try restarting the timer from 0 from the context menu and make sure the timer restarts and starts counting up.

[shefalijoshi]

Unable to test as plugin is not installed.

[charlesh88]

Unable to verify Testathon 11-15-21

[shefalijoshi]

Verified fixed.