Add icons for KTextEditor Document-Export, Bookmark-Remove and Formatting Text Upppercase, Lowercase and Capitalize

Summary:
This patch adds some more icons to the menus.
One in the file menu, one in the bookmark menu and some in the tool menu.

Example:

Reviewers: KTextEditor, ngraham, Kate, cullmann, dhaumann

Reviewed By: KTextEditor, ngraham, Kate, dhaumann

Subscribers: dhaumann, Frameworks

Tags: Kate, Frameworks

Differential Revision: https://phabricator.kde.org/D10509