Add Map model with data load and dump

[kwiliarty]

• [x] fix the loaddata command for glyphs to specify --app
• [x] adjust the way loaddata is called for glyphs in the migration
• [x] create glyphs.Map model with
  • id
  • [x] slug, primary key
  • [x] name
  • [x] description
  • owner, user or null
  • system, calculated column, true if user is null
• [x] add a scope for system maps
• [x] add Map to admin
• [x] add loading and dumping to the migration process
• [x] set up loading and dumping with a maps.yml file
  • [x] may require PyYAML
  • [x] set up gw-load-maps and gw-dump-maps
• [x] model tests
• [x] set up X-SAMPA in yml file