add env var PRISMLAUNCHER_DATA_DIR

[thatLeaflet]

This tells PrismLauncher to put its data in a subdir of $SNAP_USER_COMMON rather than directly in $SNAP_USER_COMMON.

This will not migrate existing user data, but seeing as this snap is still on the edge branch, this should not matter.

Edit: To clarify, this env var was introduced in 9.0, so it will not do anything in 8.4.

[ashuntu]

I'm not sure I see the benefit in nesting configuration data one layer lower. Are there conflicts you are running into at the moment with how it works now? $SNAP_USER_COMMON is for persistent app data, so I'm not sure what the problem is.

[thatLeaflet]

Personally, I think it's messy to have PrismLauncher put all its files directly into SNAP_USER_COMMON because that directory also contains your .cache, .config, etc. In theory, PrismLauncher could have a name collision with those.

This brings the snap in line with the other distribution methods which store their files in a subdir called "PrismLauncher", whether in ~/.local/PrismLauncher or ~/.var/app/org.prismlauncher.PrismLauncher/data/PrismLauncher.

[ashuntu]

Ok, that's fine, just wanted to make sure there wasn't an issue I didn't know about.