* Flags are now used to signal if the frequency_array and time_array properties need to be calculated again
* Should bring significant speed improvement

* Flags are now used to signal if the frequency_array and time_array properties need to be calculated again
* Should bring significant speed improvement

* The parameters attribute will now automatically update if source_model is changed

Simplified the waveform generator:
* renamed 'parameter_keys' -> 'parameters'
* WaveformGenerator instances no longer have all the simulation parameters attached. They are now all contained in a single dict called 'parameters'
* parameters does not require complicated setting rules
* frequency_domain_strain() no longer requires lambda expression, parameters are now stored in the 'parameters' container
* Changed the set_values(dictionary) syntax a bit