feat(localforage): add check for localStorage support

Closes #165, rejecting the .ready promise.
I tried the change but I got 4 errors, all of them with webKit...
> Warning: Task "casper:localstorageWebKit" failed.

* assertEval: localStorageWrapper should be loaded after calling setDriver()
* uncaughtError: "#driver-set" still did not exist in 5000ms
* assertEval: localStorageWrapper namespaces keys from config
* assertEvalEquals: localStorageWrapper driver is active

The only way to make the errors vanish is with the `!('setItem' in this.localStorage)` check.