That fix for AOSP/AOKP ROMs, you might want to revert to a backup to get messaging working again. Mobsters ROM doesn't need a MMS fix, unless you have Sprint.
If I remember correctly, Textra needs to be set up to receive MMS properly; you need to set up the APN settings under the advanced settings. Also, I think Textra automatically turns off the notifications and auto retrieving from the stock messenger, which might explain why you weren't getting any there either.
My suggestion would be to just reflash Mobsters ROM and if you really want to use Textra, then get the APN settings from the stock messenger and copy them to Textra.