Report costume data in sprite info reports and targetsUpdate

[rschamp]

• Unify the data reported for each target in targetsUpdate and SPRITE_INFO_REPORT. Previously the client needed to merge SPRITE_INFO_REPORT data with targetsUpdate data on the initial project load to have the full state of each target. This way the client can simply use what is in the initial targetsUpdate.
• Emit sprite info report whenever any sprite changes, so that the sprite list can display current sprite data for all sprites, not just the currently edited sprite.
• Include current costume data in sprite info, so the GUI can display the current costume/backdrop in the sprite list.

For scratchfoundation/scratch-gui#14
Required by scratchfoundation/scratch-gui#25

[tmickel]

Hmm, why did you keep around the on-initialize targetsUpdate? were we going to replace that entirely with the more chatty sprite-info-report events?

overall lgtm though, I like the toJSON!

[rschamp]

@tmickel I think eventually I will do that, and have a pass making all the events a bit more granular. I wanted to keep things relatively simple on this side since there's a lot going on in the GUI to go with this change.

[tmickel]

cool cool :)

[cwillisf]

👍