Added RepoApi tests for functions not yet tested

Change-Id: I2e45bbfdcae0cb378a376dd9ff635e1fe080378f
Added type checks to wikibase.api.RepoApi functions

Actually reflecting parameter documentation in the code instead of relying on the back-end handling.
This resolves some wrong documentation as well.
Added tests testing the minimum of parameters required by each function.

Change-Id: I4d043f5cc43852970a489014bc5c106592ccfdc3