Embed the comment editor

[Martii]

As @sizzlemctwizzle mentioned a while back embed the comment editor similar to GH.

This should be done before #601 and #735 e.g. as they are dependent upon this.

Pros:

• Older browsers, such as the Sony PS3, some "smart" phone apps, etc. (people do use internet appliances rather than a real machine), don't currently support the popup method. Just like here on GH with the popdown to logout... quite a nuisance for testing.
• Can allow reuse for Consider Ability to Edit Comments/Discussions #601 just like GH e.g. you can edit multiple posts including new ones all at the same time.
• On portable devices, even new ones, the popup blocks most of the page content especially when an on screen keyboard takes over a large portion of the viewport. Scrolling with touch on a very small area is not pleasant. Desktops usually don't have this issue. This is the most important reason.

Cons:

• May affect MD Editor: More buttons and such #168 if that's even an issue... don't think it is from my perspective... but who knows until it's done.