Added type of objects that have an addFrom method
These things implement HasFromList
Report tags for class descriptors.
Added methods for getting 'public' tag names
For simplicities sake, allow pointless constraints

Specifically, allow SeqFeat is SeqFeat
Fixes long standing bug whereby the schema was never being read
Allow ranges to specify the organism

Ranges need the organism to be fully specified - this change allows
ranges to have the format TAXONID:CHR:START..END, meaning we can
stringify arbitrary lists of ranges safely.

TODO: allow the RHS of a range constraint to be a list.