Add hook to catch hard tabs

Since we've standardized on using soft-tabs in our source code, we
should prevent new hires from accidentally committing code with hard
tabs.

Change-Id: I3b1828f445a3904c0c66023cf0ea614bcb19d5d6
Reviewed-on: https://gerrit.causes.com/17393
Reviewed-by: Shane da Silva <shane@causes.com>
Tested-by: Shane da Silva <shane@causes.com>