New branch "subsystems"

[robertobucher]

This new branch is an attempt to implement "subsystems" in pysimCoder. There are a lot of modifications compared to the previous versions:

• dgm files are now saved into a json format instead of the previous xml format. Files are in this cases more readable because the saved file is a Python dictionary.
• The files are saved in the new format and they can no more be opened by the previous versions of pysimCoder!
• Subsystems can be created by selecting more than one block and using the popup menu of the right mouse button
• It is possible to reopen a sysbsystem and it is possible to modify it internally. Modifications should be reloaded explicitly!
• It is not possible to add input or output ports to the subsystems yet!

A lot of tests are now required (I've implemented the code in this last 2 days...) !

[robertobucher]

For better handling of the versions, I've renamed the branches as

• mydev -> testing
• subsystems -> unstable

[robertobucher]

Subsystems are now in the testing branch. I've tested subsystems with my real applications (inverted pendulum etc.), and they work without problems. Subsystems in Subsystems are also possible