Improve the UI of Comments: Annotate button inline

Proposal link: https://design.xwiki.org/xwiki/bin/view/Proposal/CommentsAnnotations#HProposal231:Annotatebuttoninline

Proposal: When selecting a piece of text in view mode, the user can see an icon in upper corner of his selected text.
Looking like:

Behavior details:

When selecting a piece of text in view mode, the user should see an icon in the upper corner of his selected text.
When clicking that specific icon, the user can add an annotation.
The CTRL + M keyboard shortcut is kept as a functionality.
The icon should showcase the idea of adding a mention/note/comment very clearly. The "note" icon in FA is not as clear in that sense, so I would incline to using a comments icon. This icon should be added to the XWiki IconTheme.