Add simple http auth and fix custom endpoints

The client now accepts a tuple with username and password as argument on

In the work of adding this it was noticed that the client overwrote the
default values for the endpoints with None if they were not specified.
The client now correctly overwrites the defaults only if alternatives are
given. The tests have been modified accordingly.

Added more default values to example-config.json
3 jobs for feature/simpleauth in 31 seconds (queued for 2 seconds)