Drop remastersys for debootstrap + fakechroot

remastersys is no longer required to create an ISO, instead debootstrap creates
the basic environment, then fakechroot and fakeroot are used to install
packages and copy files.

Overview of the new process:
 1. install.sh is called by the user, with a path to the work directory
 2. fakechroot + fakeroot are used to invoke install.sh again, --second-stage
   1. debootstrap runs, creating a base environment in $workdir/chroot
   2. chroot is used to invoke install.sh inside the chroot, --third-stage
     1. packages and Karoshi files are installed as before
   3. final cleanup occurs
   4. filesystem.squashfs is generated, followed by the ISO itself

pre-commands and post-commands have been replaced with hooks, defined in
install/hook. See install.sh for details

Other changes:
 - the 'administrator' user has been replaced by a 'karoshi' user
 - new PPAs with updated software are configured:
   * Gimp PPA
   * LibreOffice PPA
   * MariaDB PPA
   * VirtualBox PPA
   * WebUpd8 PPA
   * Wine PPA
 - the installer has a background now, thanks to gnome-settings-daemon
 - a new utility, cleanup.sh, is available
   * this library provides cleanup and error handling functionality to any
     scripts that source it. it could be used heavily in place of exitfunc
     in set-network (see #69)
 - ifconfig dependency has been completely dropped, and is no longer installed
   * as much as possible, /sys/class/net is used to gather information