AppImage for testing

[probono]

By using CentOS 6.7 as the build system and using Qt from REPEL, the
AppImage can now run on more systems, including debian oldstable.

These are the 64-bit ones I tested the AppImage to run on:

* CentOS-6.7-x86_64-LiveCD.iso
* CentOS-7.0-1406-x86_64-GnomeLive.iso
* CentOS-7-x86_64-LiveGNOME-1503.iso
* Chromixium-1.5-amd64.iso
* debian-live-8.2.0-amd64-cinnamon-desktop.iso
* debian-live-8.2.0-amd64-gnome-desktop+nonfree.iso
* elementary_OS_0.3_freya_amd64.iso
* Fedora-Live-Desktop-x86_64-20-1.iso
* Fedora-Live-Workstation-x86_64-22-3.iso
* Fedora-Live-Workstation-x86_64-23-10.iso
* kali-linux-2.0-amd64.iso
* trisquel_7.0_amd64.iso
* ubuntu-12.04.5-desktop-amd64.iso
* ubuntu-14.04.1-desktop-amd64.iso
* ubuntu-15.04-desktop-amd64.iso
* ubuntu-15.10-desktop-amd64.iso
* ubuntu-gnome-15.04-desktop-amd64.iso
* ubuntu-gnome-15.10-desktop-amd64.iso
* wily-desktop-amd64.iso
* xubuntu-15.04-desktop-amd64.iso

And just for fun some 32-bit ones as well:

* CentOS-6.4-i386-LiveDVD.iso
* CentOS-6.5-i386-LiveCD.iso
* CentOS-6.7-i386-LiveCD.iso
* debian_7.0.0_wheezy_i386_20130705_binary.hybrid.iso
* debian-live-7.5.0-i386-gnome-desktop.iso
* Fedora-Live-Design-suite-i686-20-1.iso
* Fedora-Live-Desktop-i686-19-1.iso
* Fedora-Live-Desktop-i686-20-1.iso
* Fedora-Live-Xfce-i686-20-1.iso
* kali-linux-1.0.7-i386.iso
* tails-i386-1.5.iso
* ubuntu-11.04-desktop-i386.iso
* ubuntu-12.04.2-desktop-i386.iso

The AppImages I used are here:
https://github.com/probonopd/AppImages/releases/tag/1