Implement page generator.

[andy840119]

Part of #1766
Because all of the generators currently is for lyric only.
So need to make the new structure for able to support other input/output properties.

Also, all generators for now will clear the exist property, but it might have request not to clear them.

[andy840119]

The config for the generators:

• Min Accept time
• Max accept time

The config in the UI

• Min accept time
• Max accept time
• Clear(or Reset) the current pages.

[andy840119]

Should re-design the generator location:

• Beatmap
  • Pages
  • ClassicLayout
• Lyric
  • Laguage
  • Notes
  • ReferenceLyric

[andy840119]

And note that we already have the GeneratorSelector
Should rename to the LyricGeneratorSelector
Each type (lyric, beatmap) should have different generator selector structure.

[andy840119]

todo:

• should deal with the case with page already.