ORM, database schema setup, grant/revoke

• complete ORM (object-relational mapping) for the Chado modules 'General', 'Cv', 'Organism', 'Pub', and 'Sequence' according to Gmod
• ORM for main table of Chado 'audit' module
• Hierarchical structure of classes for database access, modification and setup in modules 'ddl' and 'io'
• New way to set up the database using 'chado admin setup'. Option '-s basic' sets up the public schema from the ORM. Option '-s audit' sets up an audit schema, with all tables automatically created from the ORM of the corresponding data tables. Option '-s gmod' sets up the database according to the current GMOD schema (default)
• usage of the ORM for implemented database operations INSERT, DELETE, UPDATE
• restructuring: 'chado list' and 'chado stats' merge into 'chado extract'
• bind parameters for pre-compiled queries ('chado extract')
• grant/revoke access privileges with 'chado admin grant'/'chado admin revoke'
• unit tests for all changes, including the entire ORM
• use new feature Ontology.typedefs of the pronto library to handle relationship-type CV terms ('typedef' stanzas) in the obo input file for ontology import
• use relative instead of absolute imports for all internal modules
• move the entry point (chado_tools.py) into the 'pychado' module