Move xblock tagging model import into method.

cms/lib/xblock/tagging/tagging.py

@@ -13,8 +13,6 @@ from edxmako.shortcuts import render_to_string
 from xmodule.capa_module import CapaModule
 from xmodule.x_module import AUTHOR_VIEW
 
-from .models import TagCategories
-
 _ = lambda text: text
 
 
@@ -30,6 +28,8 @@ class StructuredTagsAside(XBlockAside):
         """
         Return available tags
         """
+        # Import is placed here to avoid model import at project startup.
+        from .models import TagCategories
         return TagCategories.objects.all()
 
     def _get_studio_resource_url(self, relative_url):