Add signal generators

The following signal generators should be added:

• Gaussian random
• Uniform random
• Load from file

added Signal generator label

mentioned in merge request !174 (merged)

marked the checklist item Gaussian random as completed

marked the checklist item Uniform random as completed

assigned to @ollha42

changed milestone to %Lab trial

@ollha42 this is what remains. Please add the corresponding GUI config (move the existing as well).

mentioned in merge request !232 (merged)

closed with merge request !232 (merged)