Fix plaintext mode for mentionable

Also slight refactors to it.
Merge pull request #4831 from MrZYX/fix_plaintext_mentions

Fix plaintext mode for mentionable
port publisher and bookmarklet to bootstrap
Use a button instead of input to submit, use smaller photos
Refactor publisher
use fixture
Merge pull request #4678 from svbergerem/port-publisher-bootstrap

Port publisher and bookmarklet to bootstrap
Fix different button sizes in new publisher
Merge pull request #4844 from svbergerem/new-publisher-fix-button-height

Fix different button sizes in new publisher
Show hovercards in the notification drop-down for users on the same pod
Fix atom feed for reshares of deleted posts.

Propose for fix #4638

Added Changelog line

Added Specs for testing if the reshared origin post is deleted and therefore not shown in the atom feed
Merge branch 'MatrixCrawler-4638-Atom-Feed-Error' into develop
Merge pull request #4843 from svbergerem/4228-hovercards-same-pod

Show hovercards in the notification drop-down for users on the same pod

Conflicts:
	Changelog.md
Merge branch 'develop' into social.mrzyx.de