Comments support

[juliusknorr]

• Resolves: Comments [$120 awarded] #10
• Target version: master

Summary

This adds suport for comments on cards

TODO

• Unified timeline view
• Show comments in activity list
• Editing comments
• Deleting comments
• Show avatar instead of activity entry with subject
• @-mentions
• Notifications on mentions
• Code cleanup
  • Move content editable directive to dedicated file
  • Properly inject the comment manager in CardService and DeckProvider
• Tests

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Documentation (manuals or wiki) has been updated or is not required

[juliusknorr]

Move this to a separate file

[codecov]

Codecov Report

Merging #632 into master will decrease coverage by <.01%.
The diff coverage is 70.58%.

@@            Coverage Diff             @@
##           master     #632      +/-   ##
==========================================
- Coverage   76.07%   76.06%   -0.01%     
==========================================
  Files          57       58       +1     
  Lines        2474     2574     +100     
==========================================
+ Hits         1882     1958      +76     
- Misses        592      616      +24

[juliusknorr]

This PR also introduces a unified tab for comments/activity as discussed in nextcloud/server#658 / nextcloud/server#10289

• How should the tab be called, maybe "Timeline"?
• How should we handle deleted comments. In my oppinion they should still appear in the activity history, but it doesn't make sense to show them in the combined view.

@nextcloud/designers Some feedback on the design would be great.