STCC-318 and 317 Convert Hide/Show Variable [TN]

[TauBossss]

I refactored the Hide/Show Variable block. It was previously done with a workaround, now these two bricks exists.
Before merging read this:
The problem is that the previous mentioned workaround still is active for Hide/Show lists and for the monitors. These bricks are not available in Catrobat. This can result in a not very good converted Catrobat project, if a lot of monitors with text are used.

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