Various editor-related fixes

Updated the resource icon to something more data-related (was a character in t-pose).
Now appears as "Simple Data" (with a space) in the Add Component menu.
Newly-created Simple Data components are assigned the name untitled.
Added property validation to ensure name has a value.
Invalid properties are now reported as clickable build errors.
Added a shared.simpledata referenced component to the example.

Defer loading of the protobuf class until register-resource-types is called.
Removed unused aabb output.
Removed handling of unused dep-build-targets.
Deleted unused low-resolution icons.
Got rid of a few references to Spine (presumably from the editor code being initially based on the Spine editor plugin).
Moved things around in simpledata-ext.clj so code that involves protobuf field names is close together in the file.
Some minor code cleanup.

defold / extension-simpledata