New WYSIWYG editor for forums and other places

[ffont]

As a user I want to be able to write forum posts, sound descriptions, comments, pack descriptions, sound signature, profile description and private messages with a modern WYSIWYG editor so I can format content properly and feel great

As a user I want my WYSIWYG editor to allow easily adding images in my forum posts, sound descriptions, etc.

As a Freesound maintainer I want to be able to limit capabilities of WYSIWYG in specific pages or for specific users so that, for example, I can restrict image uploads to trusted users who have uploaded sounds in the past

Given that we are updating the full Freesound interface, it sounds like this is a good time to incorporate a WYSIWYG editor. Preferably, we want to re-use some existing editors for Django. @bdejong pointed to a link with a comparison of WYSIWYG editors for Django, and specifically mentioned an editor form the list which looks promising.

As can be derived from the user stories, the editor should have capabilities for uploading images, but we should be able to limit this capability to some users.

Ideally, we want a Github-like editor, supporting markdown formatting as well :)

[ffont]

Or instead, at least, add markdown support :)