Rolling back the code to 1.20 because of issues with re-binning the human Y chromsome density values resulting in a -ve value.

Commit moved to HEAD from branch-64. Moved the slice fetch into the knowngenedensity/genedensity loop so we can continue to use shift to iterate through them

the is_current field is not updated.

as records for old release are still set to current
Added query for species with new variation positions, using new field added to changelog
'variation_pos_changed'

production database.

Many improvements to reduce memory usage. Now uses registry, so don't need to specify databases explicitly, just use e.g. -species human

Fixed bug that showed up on Y chromosome and problem with not deleting entries when no analysis description was present, see release 58 notes for more details.