Add form elements to Agora

This change includes:
- Input text/password fields
- Checkboxes, Radio Buttons, and their labels
- A vertical form layout class

It also touches a few other areas that support form elements.

See a demo here:
http://codepen.io/munaf/pen/hfJLt

Patch 2:
Changed default size of input text.

Patch 3:
Restructuring to minimize the number of classes the end-user
has to apply to forms. Applying mw-ui-formlist to a ul results in
auto-inheritance of field styling. See the CodePen example.

Patch 4:
Rebasing to master

Patch 5:
Ensure sub-elements of labels aren't bolded

Patch 6:
1. Increased font size of forms
2. Edited Makefile to output comments to CSS
3. Converted utilities to mixins and prefixed with mw-ui-*

Patch 7:
Cleaned up trailing whitespace.

Change-Id: Ic37f1c02dc528fa78232857b39a7c986e5e8927f