Split bindings generator into a separate executable

[Artur K.]

The current procedure of enabling c# is a bit cumbersome:

• Enable mono module, but keep MONO_GLUE_ENABLED define as disabled
• build editor
• run editor with --generate-mono-glue PATH_TO_GLUE_DIRECTORY
• set MONO_GLUE_ENABLED to defined/true and rebuild the editor.

The saner approach would:

• build the mono-glue generator executable alongside the editor dll
• Mono module would be a DLL, so that editor does not depend on it.
• The build system would know that Mono module depends on the generated glue files.