Use source topics from Meta for comments

[erlend-sh]

Every document has a corresponding source topic on Meta. We could point to these for comments (provided the topic is open) at the bottom of every document.

• Comments could be embedded, or;
• We merely display link to comments

The ability to "Compose a new pre-filled topic via URL" might come in handy here.

[trident523]

#30 should work if we are allowed to embed comments in meta's settings. Linking to the comments would just have us change the documentation-source div to a link.

This div can now be set to display-none. IF there's another approach that should be taken to this, just let me know.