Improvements of "my videos" page

[LukasKalbertodt]

• Make event metadata editable directly in Tobira #371
• Make ACLs of events and series editable #356
• Add filtering/searching capabilities to "My Videos" #403
• Show public links of your video (where it's embedded + under username, e.g. /@peter/v/123)
  • Instead of just showing referencing realms, show video links. And also make direct link less prominent? What link do we want people to share?
• On the public/normal video page, if the user can edit the video, show a button "manage video" to get to the /~manage/videos/123 page directly.
• Maybe add note to the top saying that all videos which one can edit are shown. This is to avoid users asking the support "that's not my video!". Or generally adopt a different "user <-> video" association.

Less important

• Bulk operations (e.g. delete multiple videos at once)
• Maybe scroll to the top on pagination

[dagraf]

Further improvements > Urgency = Important

• Make it possible to search for only the videos in the page "my videos"
• Offer addtional column "Series"
• If a user does access the page "Videodetails" of a video by hitting the button "manage video", don't show the back button to "My videos" (because that's not where the user is coming from). Instead show a real "Back" button or the normal navigation of the "Administration" page.

[LukasKalbertodt]

I split this issue into multiple single ones for easier tracking:

• Add column "series" to "my videos" #530
• Add note to "my videos" explaining that all writable videos are listed #529
• Improve "share video" link in "my videos" #528
• Switch to offset-based pagination for "my videos" #527

I ignored the "less important" things in my top comment for now. There are plenty of other things one could do anyway. We will just create issues once they come up/are needed.