Refactor API URL creation in JS to new function.

URLs for the API are created three times within JS, all using the same base URL, and same action on the data to send. This makes it ideal to conceal this implementation within its own function, leaving the usage of it much cleaner.
Fix incorrect JS object
Create a common object for functions used across admin-specific objects.

Rename instantContent to instantContentSearch to mirror the naming of other admin-specific objects.

This frees up instantContent to be the common object for utility functions.
Move license status and terms check logic back into PHP.

The JS was simply checking two instantContentL10n values and returning true or false. There's no need for this logic to be done multiple times within JS - it can be checked once in PHP, and a result passed directly through to JS.
Ensure library ajax failure uses the correct callback.
Improve documentation for JS.
Refactor out building of specific API URLs into their own functions.
Merge pull request #12 from GaryJones/develop

JS improvements.