Integrate taxonomy to database

Description

This integrates NCBI taxonomy to the DB. It performs:

• Creation of all taxonomy entries
• linkage to direct parental node
• generation of full parental hierarchy from a given node

Test to be done:

• Run the import script of the full database

Closes #23

backend/metagenedb/apps/catalog/admin/__init__.py

 from .gene import GeneAdmin
 from .function import FunctionAdmin, KeggOrthologyAdmin
+from .taxonomy import TaxonomyAdmin
 
 
-__all__ = ['GeneAdmin', 'FunctionAdmin', 'KeggOrthologyAdmin']
+__all__ = ['GeneAdmin', 'FunctionAdmin', 'KeggOrthologyAdmin', 'TaxonomyAdmin']