Adding docx extension

Adding docx extension so files of docx format can be attached by email
Merge pull request #1253 from willmorgan/patch-1

Adding docx extension
API Handle uncaught ValidationException on controller execution

This removes the need for a lot of boilerplate code
around DataObject->write() logic, and avoids generic 500 errors
on user-level failures. This should really be a per-project choice,
but at the moment request handling doesn't allow to configure
custom exception handling.