Fix infinite recursion in config endpoint

[mgwozdz-unicon]

• The bidirectional relationship between PlatformDeployment and LtiContext led to an infinite recursion in the JSON output from the GET config endpoint, making the output difficult to read, making it take longer, and preventing the entire set of PlatformDeployment configurations from being retrievable via this endpoint. Removing the context field from this JSON output has resolved those three issues.
• Pagination was added to the GET config endpoint so that when the configuration database table grows to be large, its entirety is not fetched at once when the GET config endpoint is called, leading to slow requests. Pagination can be used by adding ?page=1 to the end of the request.

[ddelblanco]

Cool. I thought that infinite loop was solved, but maybe some changes reverted it. Good to have it solved And the pagination thing is a good improvement!