Desktop file generation / maintenance

[takase1121]

It may be useful if we can select what version of Lite XL to run (I think this can be done with lpm lite-xl switch, but I never got it working), and have lpm manage a desktop file that runs the correct version.

[Guldoman]

Ideally a normal user shouldn't have multiple Lite XL versions installed at once.
Other than that, no need to generate desktop files, just use lpm run as the command (eventually also using the bottles system to specify one).