Summary: Adds tootip, different icons depending on checked state and fixed functionality

Test Plan:
- Open a document
- click bookmark action
- the bookmarked page should appear in the bookmarks tab of the contextDrawer

Reviewers: #okular, #plasma:_mobile, ngraham

Reviewed By: ngraham

Subscribers: ngraham, okular-devel

Tags: #okular

Differential Revision: https://phabricator.kde.org/D22904