Add 'select all' when batch tagging

[whyboris]

User requested. Seems simple enough -- add a button in the manual tags tray ✅

[jamesd35]

Hi, can I work on this feature?

[whyboris]

Thank you 🤝

I'm sometimes rather particular about the UI (user interface), so don't worry too much about making things look great / harmonious with the rest -- I can fix it up after your code merges in 👍

Please feel free to reach out with any questions -- I'm happy to help 🙌

[TheTacoScott]

Only suggestion for an addition here is: make the same button become "deselect all" once it has selected all, and maybe have the button have the format of "deselect all (<number_of_videos_selected>)" so we have a better understanding.

[TheTacoScott]

You can see an example of the poc I did for this here: #482

although I'm not leveled up enough with angular to know how to pass down/bubble up the selected count to the right scope, but that's a solvable problem.

Also, I have tweaked the css to make the buttons look reasonable BUT they should probably be put in their own dive and made inline-block. But tbd.

[whyboris]

Currently the deselect all can be accomplished by toggling the batch mode off.
I'm unsure about cramming too many buttons into the menu, but maybe deselect all is a worthwhile addition 🤔 thank you!
I especially like the "number selected" indicator 😁

[whyboris]

Thank you for the PR! I'll try to get to it this weekend 😁
No worries about CSS -- I'll get it to look harmonious with the rest of the app (according to my sometimes-picky preferences 😅 )

[whyboris]

Thank you @jamesd35 for the feature addition #446 🙇 🎉 🤝 🦾

Cheers 👋