add taxonomy and functions API

backend/metagenedb/api/catalog/urls.py

 from django.conf.urls import url, include
 from rest_framework.routers import DefaultRouter
 
-from metagenedb.api.catalog.views import GeneViewSet
+from metagenedb.api.catalog.views import FunctionViewSet, GeneViewSet, TaxonomyViewSet
 
 
 api_router = DefaultRouter()
+api_router.register(r'functions', FunctionViewSet, base_name='functions')
 api_router.register(r'genes', GeneViewSet, base_name='genes')
+api_router.register(r'taxonomy', TaxonomyViewSet, base_name='taxonomy')
 
 
 urlpatterns = [

backend/metagenedb/api/catalog/views/__init__.py

+from .function import FunctionViewSet  # noqa
 from .gene import GeneViewSet  # noqa
+from .taxonomy import TaxonomyViewSet  # noqa

backend/metagenedb/api/catalog/views/function.py

+from rest_framework.viewsets import ModelViewSet
+
+from metagenedb.apps.catalog.models import Function
+from metagenedb.apps.catalog.serializers import FunctionSerializer
+
+
+class FunctionViewSet(ModelViewSet):
+    queryset = Function.objects.all()
+    serializer_class = FunctionSerializer
+    lookup_field = 'function_id'

backend/metagenedb/api/catalog/views/taxonomy.py

+from rest_framework.viewsets import ModelViewSet
+
+from metagenedb.apps.catalog.models import Taxonomy
+from metagenedb.apps.catalog.serializers import TaxonomySerializer
+
+
+class TaxonomyViewSet(ModelViewSet):
+    queryset = Taxonomy.objects.all()
+    serializer_class = TaxonomySerializer
+    lookup_field = 'tax_id'