Allow starting without installed apps.

biscuit/core/util.py

@@ -4,7 +4,12 @@ from typing import Sequence
 def get_app_packages() -> Sequence:
     """ Find all packages within the biscuit.apps namespace. """
 
-    import biscuit.apps
+    # Import error are non-fatal here because probably simply no app is installed.
+    try:
+        import biscuit.apps
+    except ImportError:
+        return []
+
     pkgs = ['biscuit.apps.%s' % i[1] for i in pkgutil.iter_modules(biscuit.apps.__path__)]
 
     return pkgs