Introducing fast edit

[joffreyjaffeux]

As of today it’s now possible to edit a small selection of a post in few clicks.

Can be disabled with the site setting: enable_fast_edit

Important:

• If the code is not able to define with certainty which part of the post should be edited, it will fallback to open the composer.
• It doesn’t work with discourse-encrypt ATM

Future improvement:

• a keyboard shortcut Add keyboard shortcuts to Fast Edit

Built with @Falco @sam @dan @tgxworld and @pmusaraj