added in basic version checking for server

Basically, all API requests have an optional `client_version` query parameter. 

If this parameter isn't specified, the request goes through as normal. 

If it is specified, the supplied `client_version` parameter needs to match the `CLIENT_VERSION` in the settings file of the server. If it doesn't, the server returns a `403` error with the correct client version number in the returned JSON.

Currently, the client has a string `VERSION` at the top which is tacked onto all requests. Right now, the code to actually fetch the newest version from the stuff Stephen has set up doesn't exist.

@Some3141 please take a look also.