Added configurable default options

[aleksihakli]

Hey,

I added some configurable options with a provider that creates usSpinnerConfig object. You can now configure defaults for any spinner on application startup, they can still be overridden with the directive options. Karma tests are included in the PR.

Example of configuration:

angular.module('myApp', ['angularSpinner'])
  .config(['usSpinnerConfigProvider', function (usSpinnerConfigProvider) {
    usSpinnerConfigProvider.setDefaults({color: 'blue'});
  }]);

[coveralls]

Coverage decreased (-3.75%) when pulling 0480017 on aleksih:master into 4fbaeed on urish:master.

[aarr0n]

+1 for this to be merged; would be extremely useful!

[urish]

Thanks!

[aarr0n]

Sweet!