Add CHANGELOG

Backfill the changelog file using the git history. We'll be keeping this
up to date from now on.

Change-Id: I1af3922ef5ec9804bd4d59df16e0183bb4d87b8a
Reviewed-on: https://gerrit.causes.com/33027
Reviewed-by: Shane da Silva <shane@causes.com>
Tested-by: Shane da Silva <shane@causes.com>