Use pkg_resources to determine package versions

and always add `app_version` to global template context.  this was for
sake of "About This App v1.0.0" style links in custom page footers

tailbone/subscribers.py

@@ -28,6 +28,7 @@ import six
 import json
 import datetime
 import logging
+import pkg_resources
 import warnings
 from collections import OrderedDict
 
@@ -168,7 +169,11 @@ def before_render(event):
 
     renderer_globals = event
     renderer_globals['rattail_app'] = request.rattail_config.get_app()
+
     renderer_globals['app_title'] = request.rattail_config.app_title()
+    pkg = rattail_config.app_package()
+    renderer_globals['app_version'] = pkg_resources.get_distribution(pkg).version
+
     renderer_globals['h'] = helpers
     renderer_globals['url'] = request.route_url
     renderer_globals['rattail'] = rattail

tailbone/views/common.py

@@ -24,8 +24,8 @@
 Various common views
 """
 
-import importlib
 import os
+import pkg_resources
 from collections import OrderedDict
 
 from rattail.batch import consume_batch_id
@@ -108,8 +108,7 @@ class CommonView(View):
             return self.project_version
 
         pkg = self.rattail_config.app_package()
-        mod = importlib.import_module(pkg)
+        return pkg_resources.get_distribution(pkg).version
-        return mod.__version__
 
     def exception(self):
         """