Add Explanation of some Utilities to User Guide

[Scienfitz]

Adds explanations for these utilities:

• estimate discrete space memory size
• control reproducibility via random seeds
• adding fake targets and parameter noise

Note: This required some adjustment of the code execution test. It seems that list comprehensions called via exec have some weird scope, causing NameError for NumericalDiscreteParameter even though it was imported int he code block. So I am now providing a custom dict as globals and locals arg to exec which seems to unify the scopes. As far as I know this should still maintain isolation between separately tested code blocks.