Add try/catch block to prevent chrome from crashing - fixes #57

Chrome crashes as described in #57 (similar to #9) when you check the following checkbox and load ngStorage in a cross domain iFrame:
![Chrome Security Settings](http://i.stack.imgur.com/B02MA.png)

It prevents the whole AngularJS application from bootstrapping:.

<pre>
Error: Failed to read the 'localStorage' property from 'Window': Access is denied for this document.
    at Error (native)
    at Object.<anonymous> (https://rawgit.com/gsklee/ngStorage/master/ngStorage.js:42:41)
    at Object.d [as invoke] (https://code.angularjs.org/1.1.5/angular.min.js:28:304)
    at https://code.angularjs.org/1.1.5/angular.min.js:30:39
    at c (https://code.angularjs.org/1.1.5/angular.min.js:27:142)
    at d (https://code.angularjs.org/1.1.5/angular.min.js:27:276)
    at Object.instantiate (https://code.angularjs.org/1.1.5/angular.min.js:28:434)
    at https://code.angularjs.org/1.1.5/angular.min.js:53:326
    at https://code.angularjs.org/1.1.5/angular.min.js:44:274
    at n (https://code.angularjs.org/1.1.5/angular.min.js:7:74) 
</pre>