New gems support

New features:

• Query card data on demand, reduce network traffic ( /pull/3, /pull/4, /pull/6, /pull/7, /pull/9 )
• New skills (AC card) format support ( /pull/5, /pull/6 )
• 4x play support for llactivity ( /pull/15 )
• LP discount support for llactivity ( /pull/19 )
• Arcade song support ( /pull/27, /pull/30 )
• New gems support ( /issues/21 )

Develop enhancements:

• Unified many duplicated code (song selection, card selection, strength calculation, skill text, etc.)
• Decouple load unit logic from backend server and unify save data format conversion
• Support SIF 6.2 db format

Bug fixes and small enhancements are not listed here.