Allow wrapping a remoting object

Updated `Premote.wrap` to accept an entire remoting class object:

```
// original syntax, still works:
var promisedUpsert = Premote.wrap('myClass.upsertThis');
promisedUpsert(account)
.then(doSomethingOnSuccess);

// new syntax
var promisedClass = Premote.wrap(myClass);
promisedClass.upsertThis(account)
.then(doSomethingOnSuccess);
```