Should be able to save beatmap into json format in the editor.

[andy840119]

For able to test the editor more convenience.

What expected to added:

• Save
  • Override the beatmap content
  • Create new difficulty
• Export
  • Export to json format
  • Export to json beatmap

Not very sure add those functions into ExportLyricManager
Or create the another class (e.g. Edit/Debug/DebugBeatmapManager)

[andy840119]

Implemented.