Add maxBy
Add maxBy

While only a special case of maximumBy, it is useful
to have this total function (as the signature ensures
two arguments). Also this signature fits better operations
like insertWith.

Signed-off-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>
Reviewed-by: Petr Pudlak <9d19625f8ee825a2c398462ed335cbcf98f79c32@google.com>

leshchevds/ganeti,mbakke/ganeti,bitemyapp/ganeti,onponomarev/ganeti,mbakke/ganeti,leshchevds/ganeti,bitemyapp/ganeti,andir/ganeti,andir/ganeti,ganeti/ganeti,ganeti/ganeti,mbakke/ganeti,ganeti/ganeti,onponomarev/ganeti,andir/ganeti,leshchevds/ganeti