[iOS] Download error failure handling

[Developer] Add kmlmc command line compiler and environment

[Android] Disable version and copyright text from flashing on splash screen

[Developer] Lexical model compiler CLI

[Developer] Better compilation assertions

Addresses #1964

Fixes iOS Get Started

[Developer] Add basic file format support for lexical model packages to Developer

Move the reference line to the compiler. Now the model.ts file doesn't need to know about that either!

[Developer] Reorganize developer/js with a more conventional file structure