Create an `Installer` class & make InstallerMedia inherit from it.
Let's create an Installer
class, which InstallerMedia and (the soon to be created) InstallerTree are going to inherit from.
Methods like live()
and eject_after_install
should just return false
for the InstallerTree.
Other methods receiving an InstallerMedia
should also be changed so they could receive an Installer
instead.