Change endpoint responses where there are marshalling, unmarshalling

or param errors to raise invalid data exception. That will cause
those responses to be handled in by errors.py, which will log
the errors.

Set most of schemas to strict mode so that marshmallow will raise
exception rather than checking for errors in return tuple from load.

Added handler to errors.py for marshmallow validation errors.

tests/app/dao/test_templates_dao.py

@@ -267,6 +267,6 @@ def test_get_template_versions(sample_template):
             assert x.content == 'new version'
         else:
             assert x.content == original_content
-    from app.schemas import (template_history_schema)
+    from app.schemas import template_history_schema
     v = template_history_schema.load(versions, many=True)
     assert v.__len__() == 2