chore: Update FiraSans to v3.1

FiraSans v3.1 is packaged in connect-fonts-firasans@0.0.3

fixes #1199
Merge pull request #1222 from mozilla/issue-1199-firasans-update

chore: Update FiraSans to v3.1
chore: Remove font dependencies from bower.

* Fonts are installed via npm and copied to the correct location using grunt.

fixes #1230
Merge pull request #1233 from mozilla/issue-1230-font-bower-deps

chore: Remove font dependencies from bower.
fix(forms): labels should not shift unless values change

Fixes #1008.
Extract lib/floating-placeholder-mixin.js from views/form.js.

* Add unit tests.
* Update dependent modules.