xemu: enable 'portable' app data storage

[Mahir007]

Currently, xemu installed through scoop stores data outside the scoop directory.

This is the case even though xemu supports portable mode.

Therefore, it's a good idea to add portable mode support to the xemu package to keep the emulator in-line with the persistent data storage expectations of scoop.

[Calinou]

Feel free to open a pull request for this 🙂