WIP: Implement comment posting (and reenable voting)

This is a work in progress for adding support for posting comments to the KNewStuffCore framework, and cleaning up voting a touch. It further adds UI for creating said comments to KNSQuick.

• Add signals to fake a virtual function for posting a comment
• Implement comment posting (and userCanVote check)
• Add invokable functions for creating comments (and reviews)
• Add voting function to the quickitemsmodel (and userCanVote role)
• Entry details checks for voting ability
• Don't allow voting from the list view (in the old dialog)
• Allow clearing the Rating control when it's editable
• Add vote requesting feature to the Rating control (separate from editable), to allow the user to vote without changing the existing value (which should be updated elsewhere)
• "New Comment" component created to allow making new comments, replies to comments, and reviews
• Added New Comment to the entry comments page, and replying to the comment delegates
• Added New Comment to the entry details page, which can be activated when an entry has no comments already
• Add reply request functionality to the comment delegate
• Add calls through to Attica for requesting editing of user credentials (which uses the code in D25961, which launches the kaccounts kcm to allow the user to log in to their opendesktop.org account)
• If the user is marked as not allowed to vote, attempting to comment or vote will request the credentials editor

This does not strictly require plasma/plasma-desktop!66 (merged) , but without it this will simply not allow voting and commenting with the attica backend

This was originally worked on at https://phabricator.kde.org/D26794 BUG:418995