Save content of sound/particle files in bbmodel file

[SAGESSE-CN]

Detailed description of your suggestion

The current blockbench file path references:

name	description
texture	base64 encoded string + file path reference
particle	file path reference
sound	file path reference
animation	embbed json + file path reference

When save the project the it will show multiples annoying file save dialog, this forces people must provide a location to it even though it doesn't have any need.

When people share a blockbench model to other user, people must to send all additional files.

When people clean the disk to be careful the additional files referenced by blockbench model, because as time goes people forget this references.

so I hope to add an standalone file mode, all file resources are saved to blockbench model in base64 or other, and the no longer required to provide a location to it.