[Blockly][Codegenerator] Prevent use of space in variable names

[mariopesch]

Block description

You can create variables with a space in the name such as:

The result is a compiler error.

Expected block behaviour

Prevent the use of space in variable names. Either show an error during the creation process or automatically replace the space with an underscore.

[PaulaScharf]

Btw the issue also arises with other characters, not just spaces (" ' & * ...)

[mariopesch]

closed via #360