Wire sprite info panel to VM

[rschamp]

Sets up sprite info component to reflect data about the selected sprite in the panel.

In the interest of time:

• Every field is updated as you type, including x/y position. Typing - is interpreted as -1. Eventually this should only happen on blur or enter key pressed. Good luck trying to update position while a sprite is moving 🙃
• When you select the stage, the sprite info pane becomes disabled, with placeholder values set in the inputs
• Everything is handled with props passing. This is a good place for redux, but I needed it to be done for the play test tomorrow.
• I did minimal performance testing. I would not be surprised if some projects perform more slowly after this update. I believe the redux refactor could help with this, since it would reduce the number of parent components that would need to re-render as sprite info changes.

/cc @lifeinchords @cwillisf @carljbowman

[thisandagain]

Validation of Sprite Names

One issue that may be ok to resolve later if we file a bug is that it is possible in the PR to have sprites with '' as a name as well as multiple sprites with the same name. This will become important to resolve once we complete work on blocks like point towards [x] and go to [x].

Negative Integers in X / Y Position Fields

If you start typing a negative integer (e.g. -50) into the x or y position fields it will always prefix with -1 which leads to unexpected results and can be very frustrating (-50 turns into -150). This issue would probably be good to resolve before testing.

Performance

The performance hit is really quite large and you can feel it while interacting with the GUI (dragging out a block, panning the workspace, adding a sprite, or editing a field) while a simple program is running (forever [turn 15 degrees move 10 steps]). Good example:
https://llk.github.io/scratch-vm/#141490356
https://llk.github.io/scratch-gui/#141490356

[thisandagain]

I think I'm ok to land this as long as we file bugs for the three issues I listed. I recommend that the negative x/y position issue be resolved before the Friday review.

[rschamp]

I fixed the performance issues altogether! Hahahaha!

[rschamp]

And agreed on the other two points.