feat/timestamp link

[nmpereira]

closes https://github.com/labrocadabro/communitytaught/issues/58

• Added support to start the video if a query t=seconds is in the link. Example:url&t=50
• Added button on class page to copy link at current timestamp to the clipboard

Notes:

• when a user is logged into their youtube account and have youtube history enabled, the youtube history overrides the timestamp provided in the URL. In my opinion, this should be a separate issue. From working on https://github.com/labrocadabro/communitytaught/pull/65, seeking via js does seem possible. This will require another attempt in a future PR https://github.com/labrocadabro/communitytaught/blob/8b514baafa471a471bd196775f1ed241b4f13857/src/assets/js/goToTime.js#L27

screenshots

Button to copy link

Animation when button is clicked