Implement low-pass filter

[gituser789]

configurable, ready-to-use low pass filter

• generate a copy of the incoming scope object
• implement low-pass-filter, configurable
• return modified scope object
• implement unit test for this method

additionally, add derivative

• generate copy of the incoming scope object
• implement derivative, configurable
• return modified scope object
• implement unit tests for this method

Small fixes in the whole code

• lot of typos
• small datatype fixes in return/docs

[SevenOfNinePE]

For both functions:
How is the behaviour, if values are added, which leads to a negative answer of the called toolbox function m'FinDiff'. E.g. what happend in case of order=10000000. Or the angular_frequency_rad=1.2? I know, the last call is prevented, but e.g. order of 1000000 may leads to a negative answer of the calling function 'signal.butter' you prevent this). How is this situation handled. If the python raise an error and stops the program, this is ok, but if the program continues, it could be a problem.

[SevenOfNinePE]

As discussed, this it a test comment and needs to be removed.

[gituser789]

removed

[gituser789]

depending on the available datapoints, the external toolbox will stop working by ruinning into an error. Then, more datapoints are needed to do the derivation for the signal.

We can also limit the max. derivation to practical values, e.g. 2 or 3