[Forum] Add ability to quote forum message

[JLAFLASH27]

Add the ability to use quote within a fourn post.

[jannes-io]

We have the quote markup already in the rich text editor.

Add a button on each comment to "quick reply" (at the bottom of each comment on the right of reactions?), which will:

1. fill the comment textbox at the bottom of the page with the content of the original comment wrapped in a quote block
2. add a mention to the author of the original comment
3. scroll down to the comment box

Issues that we need to find a fix for:
Nested blockquotes do not work at the moment. So if you quote a post that contains other quotes, funky things happen and the blockquote gets broken up. Maybe just accept this as an issue for now and deal with it later in a separate issue?