Add pre-commit git hook for database records checking

As a developer I would like git to automatically check my db records and not let me make a commit if there is an error so that I will spend less time debugging my records.

Acceptance criteria
- DbUnitChecker needs to be called before all commits
- If there is a problem, the commit may not go ahead
- The output of DbUnitChecker needs to be routed to nul so unnecessary files are not created in the build directories
- An install script which inserts the hook in all of the submodules git hook folders which will have db files in it.

Nice to have:
- Only give DbUnitChecker the db files which have changed in this commit