v1.0-rc1-akin

Adding some polish for release:

• Help system
• Singing screen:
  • when sorting by leader, co-leads are displayed separately
  • added an message for non-Denson singings
  • long click allows you to select leader or song
• Song list:
  • when searching with a sort that has headings, headings remain instead of being replaced by the "Title" group

Bugfixes:

• graph zoom is actually disabled
• songs with key changes are counted in major percent