Add documentation for column and menu rows

[acrilique]

Putting this here to hopefully gather some criticism and let it sit for a bit.

Various things that come to my mind:

• The "Column" name is not very descriptive now that we have more context about what these do
• I could put up a list of the menus which are pointed to by content_pointer and write down their values in that field. This would make sense bc it does seem this value does point to the actual list/menu type in the player's firmware.
• Another list of the "default" menu (Column) names which are written into the db by rekordbox could be done, although imo this would be of less relevance than the previous

#dysentery & crate digger > Menu and Column pages