Support for fontcustom for canvas icons
This uses the fontcustom gem to compile our icons from svgs in the
public/fonts/ folder. No more complicated workflow for adding/editing
icons!

Way to test:
  * Add your new svg to public/font/icons/
  * Important!! Edit template file to update
    stylesheet in public/font/_canvas-icons.scss
  * Run the rake task to compile: bundle exec rake icons:compile
  * Check the styleguide to make sure they're pulling in
  * Done!

Update
fixes DES-101
-takes our core_en.js file (unneeded)

fixes DES-101
- Changes font directories
- Tweaked documentation

fixes DES-101
- Tweaked documentation
- Changed directories for font icon
- Added unique hash to font name

fixes DES-101
- Changed rake task to perform bundle exec
- Updated documentation
- Added missing config file

fixes DES-101
Takes out the default [date-icon] css fontcustom puts in

fixes DES-101

Take out all the icomoon comments in the svgs

fixes DES-101

Added missing icons to font

fixes DES-101

Adds the fontcustom gem to a different gemfile

Change-Id: I9860cb074baaf4518548c9d87c1177a14d96a44c
Reviewed-on: https://gerrit.instructure.com/36974
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Reviewed-by: Ryan Shaw <ryan@instructure.com>
Product-Review: Colleen Palmer <colleen@instructure.com>