Support word/phrase underlining/highlighting

[nramos0]

Story

• As a normal user, when reading an article I can highlight/underline a particular word or phrase in one of a few simple colors, so that I can mark that section for my own purposes.

Definition of Done

• Highlighting/underlining is separate from normal word status highlighting. Highlighting/underlining a particular word or phrase in a particular place will not highlight/underline the same word or phrase anywhere else except the original place, including the same word/phrase on the same page, a different page, or in a different article. Essentially, highlighting/underlining works like it does in real life: doing it for one word in one place will not do it for the same word anywhere else.

[nramos0]

259081702b54083b2dadeb60dcf0e8af3108bb94 ea9d8dfe1ab2d47191d2af139ad23f30620b8bb8

[nramos0]

Underlining is supported, but highlighting is not. The server supports highlighting as well (it knows these objects as a generic 'mark' which can be an underline or a highlight of a particular color over a range of words), so supporting highlighting in the frontend should not be too hard to add. The main difference is just the frontend displaying marks that are highlights differently than it currently displays those that are underlines.