[Blockly][Codegenerator] bitmap naming

[PaulaScharf]

Current Block Behavior

The block for the led matrix bitmap has a field to name the bitmap. The user has to manually give a unique name to each bitmap. If the user reuses a name the old bitmap is overwritten. I think this is confusing.

Expected Block Behavior

I propose the following:

Create a new Block to store a bitmap (like a text block). This block will not create a new global variable in the arduino code. Just like the text block also does not.

Have the draw-bitmap-block accept this as input.

Optionally: make the bitmap reusable.
To do so we need to create variables with the "Bitmap" type. Just like its possible for strings and ints and so on. The blockly code with bitmap variables could look like so: