Changes

• Fix RMG not using xwayland when using wayland (wayland has lots of issues, can be disabled by building with the -DFORCE_XCB=OFF option)
• Fix some non-fatal mupen64plus errors showing a pop-up
• Fix window not returning to ROM browser when launching a game through the commandline and the plugins aren't ready
• Add support for Qt stylesheets (place them in the <user data directory>/Styles directory with the .qss extension, they'll show up in Themes)
• Add "Icon Theme" setting
• Add "Speed Factor" to System menu bar
• Add support for re-ordering columns in the list view of the ROM browser (thank you @RetraCarteR)
• Add AppImage to github releases (this replaces the old portable linux builds on github releases)

NOTE: if you're using a portable linux build from before this release, the updater will break, you'll have to manually download the AppImage and use that instead!