writeFields method to be shared between create, update

The update method was having problems with dates passed in an object.  I looked between ngForce and remoteTK and was seeing that TK had this method as a private to be shared between anything writing fields.

I didn't do upsert yet because I haven't had a use case for it.

I also added some apex debug statements--purely for convenience.  At least for our org (public sites), it can be easier to turn on debug tracking on a user than it is to try to recreate whatever the users are doing to get the errors via the browser.  

I love you for making this!