Check type of each parameter and give clear error message on fail

[FrederikHeber]

When using the python interface, one gets confusing error message when an option is used with the wrong type. For example, hidden_dimension needs to be a string at the moment. If we use a list of strings, we get an error message.

Python options should have clear types (similar to the ones used by the command-line interface via argparse) and need to admonish if the wrong type is given,

[FrederikHeber]

I need to base the set of options that control sampling, optimization, ..., i.e. 'step_width' and so on, onto a solid base.

To this end, I refactor MockFlags into a full class.

Work has begun in branch *Abstract_Options`.

[FrederikHeber]

Implementation is now done in the following way:

• base class Options where we override __getattr__ and __setattr__ to allow the user to easily access options is if they were member variables of the class, i.e. the following works.

  options = Options()
  print(options.step_width)
  options.step_width = 0.03

• For this an option has to be enlisted before, options.add("step_width") will make it known to the class. This is not necessary but enforces the programmer to be aware of adding new options.
• derived class PythonOptions contains a flock of default options, their types, and a description. This allows to use options.help("step_width") and get a description, default value, type, and so on. Moreover, the type is checked when setting the value. Setting an unexpected type triggers an ValueError with a informative error message.
• derived class CommandlineOptions adds additional code to convert strings into the desired type, e.g. a list of integers. For example, hidden_dimension can be specified as both "2" "2" and "2 2". Both versions are converted into [2,2]. Moreover, it adds all arguments to the argparse parser, using the description, default value and type from PythonOptions. I.e. this is ensured to be consistent.

[FrederikHeber]

As this is working and Simulation_interface is merged into v0.9, I close the issue.