Report Value UI (for non-string values)

[pmalacho-mit]

Motivation: Now that custom arguments are better supported, it is possible to interact with more complex data types via scratch blocks. If this complex types are returned by Reporter blocks, then they will be printed to the screen as their String(...) value, which is not ideal (you see a lot of [Object object] type print outs).

Instead, we should add the ability to render a UI when a value is reported.

Relevant code lines:

• https://github.com/mitmedialab/prg-extension-boilerplate/blob/dev/packages/scratch-gui/src/containers/blocks.jsx#L346
• https://github.com/mitmedialab/prg-extension-boilerplate/blob/dev/packages/scratch-vm/src/engine/runtime.js#L2336