Clean up MergeableSelector docs and style

Some of the wording for the documentation was a bit off. Fix that and
some style in code and specs.

Change-Id: I7a21bf73e5c40ba35736582227bdf4d80b4aa75a
Reviewed-on: http://gerrit.causes.com/37605
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>