Fixes #102 - font awesome integration

Replaces icon images with font awesome icons. (Except for filters.)
Update canNext method

With the update to font-awesome the canNext is running before
$scope.stewards is initialized, so add a check that it’s not null.
Updates font awesome CDN URL

Font Awesome URL provided on font awesome page did not work with
Cordova. This updates the URL.
Adjusts CSS for iOS emulator
Removes unused icons
Removes unused map markers
Updates map markers
Merge pull request #106 from codeforamerica/102-font-awesome

Fixes #102 - font awesome integration