matchbox: miscellaneous fixes

Created by: duncanguthrie

The changes may be summarised as:

• Build matchbox-panel against libmatchbox with libxsettings (automatically detect if libmatchbox was built with xsettings, then build with xsettings);
• Build libmatchbox and matchbox-panel with debug symbols;
• Upgrade matchbox-window-manager and matchbox-desktop to version 2 (these now don't use xsettings, but matchbox-window-manager is built with GTK+2 support, and can have certain font configuration applied through that and e.g. its support for pango);
• Change source of matchbox-panel to Debian's source, which had miscellaneous fixes not upstream;
• Amend the terminal-launching panel-applet to look for x-terminal-emulator (e.g. if we use update- alternatives as provided in Alpine's dpkg package, we can change our terminal preference globally);
• Remove unused patches arising from changing package versions and sources.

This fixes the strange issues with Qemu and some issues I had patching the original matchbox-window-manager and matchbox-desktop.

That being said, I haven't enabled PNG themes in matchbox-window-manager, because the program would not build properly otherwise, and they are not essential at the moment.

I tried to get version 2 of matchbox-panel working, but it did not work at all. It is a shame, because this is a rewrite of the original panel with modern features like GTK+3 support. That being said, the components of matchbox now seem to be at least functional and mostly stable, and are usable on real devices.