Add non-assigned to global-variables-debugging

[Syrious]

When debugging for example an if-statement it would be nice to see the global variables in the debug menu. Please check the image. In this short example I can't see :btn in global variables and therefore I can't change its value within the debug session

[dbaumgarten]

That's exactly how I intend to solve the problems described in #74 .

The debugger should simply always list all global variables that are used somewhere in the script.

This shouldn't be too difficult to implement. Maybe I can make some progress on this tomorrow.

[dbaumgarten]

Added as part of v0.1.7