Organize changelog for 0.31.0 release

Change-Id: I38f785fdbf66a4b5a95db04d4262eaac71f323ff
Reviewed-on: http://gerrit.causes.com/45171
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>
Tested-by: Shane da Silva <shane.dasilva@brigade.com>