remove api.php from python client

[melange396]

modify the python client so it no longer uses the legacy "api.php" url.

the api.php endpoint uses some request variables differently than other endpoints do, which makes it difficult to do accurate aggregate analysis of webserver logs. the api.php endpoint also has a lower limit for the maximum number of rows returned; using appropriate endpoints directly instead will allow users to retrieve more rows in a single request.

this will require changing the BASE_URL in many of the integration tests which use the client (simple but tedious).

[melange396]

this will also necessitate changing the covidcast client at or around the same time.

[melange396]

duplicate of #1285