Refactor/Rewrite

There were a couple of issues with this plugin... 

1. Authentication seemed to expire.
1. Some sites didn't even seem to work properly on some accounts.
2. A very low number of posts was returned each query, resulting in many many API requests on larger sites.
3. I think The 3rd party API class was using an old vesion of the API

I have updated this to use the PHP class provided by Google. It does proper oAuth so should be more robust. Updated the admin to allow the user to save all the API details. 

Also update the API to return 500 results for each API request so should be much better on larger sites.

Todo - remove unused files from Google API PHP class.