[installer] [host] all systems: we only need one 'diskdevice' class for all platforms. Adjust signals and slots to account for this. On windows:
we don't unmount, as we just trash the MBR. Before writing to remove partiton entries, but we must return true in bool io::unmountDisk(QString devicePath). Add device enumeration and device imaging. Linux: remove determining if the disk is removable or not, as a USB installation on most systems still requires the SD card. However, retain ability to get installType (useful for preseeder).