Support advmess directly from MainUI with a dedicated launch.sh

[schmurtzm]

It's possible but not very easy to handle.

The command line generated by advmenu to run advmess is like that :
/mnt/SDCARD/.tmp_update/bin/adv/advmess ti99_4a -dev_cartridge carwars=carwarsg.bin -sound_volume -26 -quiet

So we need to create a script to generate this command line automatically. It will probably requires to parse advmess config files.

The advmess nomenclature is different to Retroarch :

• rom = cores in Retroarch
• image = roms in Retroarch