Make optional arguments to create_study actually optional #1110

From the docs create_study and create_benchmark_suite contain some optional parameters, e.g. alias, which don't have defaults which actually makes them required.

1. For the alias parameter a None default seems sensible.
2. For a study the suite's id is also optional, is it by design that we want studies without suites?
3. I would argue that for a study, the run_ids should also be optional as they could be created later (e.g. in a setup where you define a study, and upload results to it as they come in).