This is a rewrite of the various API invocation methods for unit tests

that simplifies them, moving all common logic to a single function

(api_call, formerly _api_func_wrapper). The various wrapper methods

now just invoke this method with some default arguments. Subclasses can

override api_call to add further logic, and the other methods will

benefit from it.
These also now allow for specifying the number of SQL queries that an

API handler was expected to have run. This is done by passing

expected_num_queries= to any of the API invocation methods.
The new methods are backwards-compatible with the old ones, so long as

the various keyword arguments (anything past path and query) weren't

passed as positional arguments. However, it does rename the query

argument to data, which makes more sense for non-GET requests. If

passed as a positional argument, nothing changes, but if passed as a

keyword argument, a warning will be emitted and the argument will be

converted.

Djblets and Review Board unit tests pass.