MOSes, better automatic layouts and color schemas

• New: Add pergen::Mos for MOS analysis
• Change: EqualTemperament is now IsomorphicLayout
• Change: PrototypeTemperament is now Genchain
• Improvement: Add Genchain::Tetracot7 and Genchain::Hanson7
• Improvement: Better implementation of the IsomorphicLayout search s.t. more and better matching layouts are returned
• Improvement: Better color schema API with support for multi-cyclic MOSes using IsomorphicLayout::get_layers
• Improvement: Retrieve MOS scale name via IsomorphicLayout::get_scale_name
• Change: layout::IsomorphicKeyboard has been merged into pergen::Mos
• Deletion: TemperamentFinder has been removed
  • Use IsomorphicLayout::find_by_{edo, step_size} instead
• Deletion PrototypeTemperament::Porcupine7 has been removed
  • Use Genchain::Tetracot7 instead