Support Unicode paths in Form.LoadProps()

[majcl]

Hello,
i added support for unicode filenames for Form.LoadProps() methods.

Initially I thought it would be short and simple, but correct work with unicode and filesystem has its quirks.
Also be conforming to python PEPs added some work.
Since there are a lot of possible exceptions and errors, i also extended support for unicode exceptions somewhat. The additional features are:

1. LoadProps now support unicode string as filepath
2. LoadProps now support bytes as filepath
3. LoadProps now support os.PathLike objects as filepath
4. Generic handler for Delphi exceptions -> Python exceptions has been added (as a mirror to RaiseError; which handles python exception -> delphi exception)
5. There was no test for python vcl/fmx libraries, so i added one file per library - though i added only tests for new unicode functionality. I know its not completely conceptual, but i didnt want to add to this PR too much new stuff and since there wasnt nothing yet... The test is runnable either standalone without any additional dependencies, or via pytest (for more nice and detailed output)

Note: I want to apologize beforehand - im not delphi pro, last time i worked more with delphi was 25yrs ago, so i want to apologize for the stupid stuff i may have made. However sometime ago i accidentaly found delphifmx and delphivcl python libraries and i was so amazed(i liked vcl a lot then), so i started to use it for my hobby project...