API Handle uncaught ValidationException on CMS 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.
Minor: Two modules are listed as three.

...for example "framework" and "cms". These three modules... Should be two modules, or perhaps there is a third missing from the list.
Fixed link and added branch direction

Broken link to edit docs, perhaps should link to repo instead of directory to avoid having a branch in the URL.  Also added blurb to clarify what branch doc edits should occur in.
Merge pull request #1263 from danrye/patch-1

Update module-development.md docs
Merge pull request #1261 from chillu/pulls/validationexception-routing-3.0

API Handle uncaught ValidationException on CMS controller execution
Merge pull request #1265 from danrye/patch-2

Fixed link and added branch direction