modularlize the code

Currently the module supports a number of the Google Provisioning API calls. Each one of these has their own function with lots of duplicated code. The attached patch creates a new drupalgapps_clientlogin_api_request() function which each of the api functions can call instead. This reduces the number of lines of code, halving the size of the module, and should make it much easier to maintain.

The patch also renames the drupalgapps variables from 'apps_....' to 'drupalgapps_...' in line with Drupal's coding standards, and removes these variables from the db in hook_uninstall().

Dependant on #685606: coding style cleanup being applied first.

Cheers,
Stella