Fix whitespace bug in password validation.

Previously called #trim on password and confirmation fields before
comparing them -- this led to 'password' and 'password ' comparing
equal.  Also in this commit:  moved the error explanation out of the
comparision function, should make it easier to factor out into library
code later on.
Client-side email validation.

Rough email validation, using the same regex as the server: /.+@.+\..+/.
In depth validation is not worth the effort, but this should catch
obvious typos, at the very least.
Factor out form styling.

Pull out common form styling (coloring, error classes, etc) into a
separate Sass file.