[Fix] Ensure custom font gets loaded when setting it

- In $scope.$watch of "font", now checking if this previously saved font was a custom font, and if so, call newly added function addCustomFont in picker
- Added function addCustomFont in picker to load a custom font, save the url, and apply value of currentFont
Merge pull request #68 from Rise-Vision/bug/set-font-custom-load

[Fix] Ensure custom font gets loaded when setting it