refactor UsersController to reduce complexity

Refactored: UsersController#create
do not select the marker in Chrome
allow plugins to be symlinked
force max-width on images/svgs in composer preview and post view

Conflicts:
	app/assets/stylesheets/desktop/topic-post.scss
FIX: Link reference-style text without a url
Add screening by IP address. When deleting a user as a spammer, block all signups from the same IP address.
Build out a URI Adapter to allow uploading an avatar via a url

Currently only really accessible via the API. The UriAdapter creates a
tempfile from a url and gives a ActionDispatch::HTTP::UploadedFile back
to the controller to process as normal.
This will help a lot in being able to transfer avatar urls from another
app without monkey patching a lot of discourse code.
Sync up with markdown-js + our changes
fixed deleted/mod post highlight, reduced some gutter padding, re-aligned some title elements, better spacing around .logo-small
Merge pull request #1557 from awesomerobot/master

fixed deleted/mod post highlight, reduced some gutter padding, re-aligne...
Merge pull request #1543 from railsaholic/small_users_controller_refactoring

refactor UsersController to reduce complexity
Merge pull request #1512 from ScotterC/avatar-from-url

Build out a URI Adapter to allow uploading an avatar via a url
differentiating visited topics better, fixing extra white space in the title header (also realigning title header)
Merge pull request #1558 from awesomerobot/master

differentiating visited topics better, fixing extra white space & alignment in header
fix images height on IE
fix code highlithing in list
fix quote reply z-order
remove bottom border on posts-wrapper
tighten up spacing on notification control