User chord set hierarchies

add support for user chord set hierarchies in support of the following use case of a huge chord pack:

gig books
  book 1
    song 1
    ...
    song 999
  ...
  book 999
    song 1
    ...
    song 999

this would allow a single pack download with large numbers of books with large numbers of songs – even subcategorized by genre, etc. of arbitrary hierarchy depth while still supporting reasonable navigational (scaler ui) and chord management (chord author) experiences…

Hi @d00d and welcome to the forum. Thanks for the feedback it is noted!