Prevent tag input field from changing height
Use ems for read only tag font size
Fix the height of the tag input

This fixes an issue where the difference in input height between
Firefox and Chrome/Safari causes the input area to jump.
Rewrite renderMath() to also parse inline math
Rewrite insertMath() to know when to apply inline vs block formating
Rewrite renderMath() function

Rewrites the renderMath() function to sanatize, render math, and render markdown.

Big thanks to @tilgovi for help here.
Fix regular expression and add MathJax fallback

The regular expression was incorrect and was matching the occurance of any backslash, but this commit fixes it as well as reintroduces the MathJax fallback.
Merge renderMath() into ctrl.$render add basic inline math support

Since renderMath() is doing much more than just rendering math, it is now a part of ctrl.$render(). This commit also adds basic support for inline math. However, this is not quite ready, using inline math inside of lists or block quotes does not yet work.
Add support for additional \\( block math \\)

Clean up code, add comments, and add CSS to hide MathJax rendered math in a collapsed annotation.
Add explanatory comments.
Fix #1573, make annotation bodies collapse correctly
Validate that email exists on forgot_password

Close #1570
Remove 'or MathML' from the text inserted on pressing the Math markdown button.
Undo fix for #1573.
Separate login errors for username and password

Close #1556
Pin sass install to work around sass/sass#1476

sass==3.4.6 has introduced a regression in the parsing of
pseudo-selectors such as

    :not(:focus)

which breaks our build. We need to temporarily pin to 3.4.5 to avoid
spurious build errors all over the place.
Add more usernames to blacklist

I noticed that root and postmaster were missing, one thing led to
another, and I added a bunch of names from this list:

    https://programmers.stackexchange.com/questions/115425/is-there-a-list-of-common-usernames-to-reserve-in-a-new-system
Remove YUI grid

It's not currently used anywhere and we could do with a cleaner grid
implementation.
Add a simpler grid system

This replaces the YUI module we had before and implements only the parts
of the system that we need at the moment leaving a far cleaner and more
readable api.
Use floats in the grid module

This works around the nasty hacks involved in removing the whitespace
between inline-block elements without having to use comments or
negative letter/word spacing.

This does mean we can't do centered or right aligned grids very easily
at the moment. If we need these things in future we can reconsider.