updates
- changed taxonomy base class and GemTaxonomy derived
  - added TaxonomyAttributeGroup to hold multiple TaxonomyAttribute
  - updated parse algorithm
- changed Statistics/StatisticNode
  - Statistics now is tree without knowledge
  - all attributes will appear in tree if specified

TODO
- build_ms dialogbox to adjust parse_order
- mod_input dialogbox to use drop-down list for building modifier
- taxonomy build string using given attributes
updates
- updated to use taxonomy v2.0
  - generate taxonomy string with all v2.0 fields (repeat direction)
  - use rules when selecting attributes in same scope
- fixed edit_attribute dialog for building taxonomy string for single attribute
  use scope to limit
- test to make sure mapping scheme is valid before creating exposure

- refactored dialog for Setting attribute range to main
- refactored attributeList out of build_ms into its own widget
  this should allow application to re-use same attribute list

- updated tests
  - updated test cases
  - updated test3.db
updates
- new tree user-interface for selecting attributes to use
  for creating mapping scheme

- refactoring
  - remove leading _ character in variable names
  - changed taxonomy.attributeGroups to taxonomy.attribute_groups