Since fixing QubesOS/qubes-issues#3213, launch function correctly waits
for some applications exit. This is undesirable for
qubes-session-autostart service, which should just start the
applications and exit.
Since we have proper python package, use it instead of hacky one-file
package. This will ease installation and packaging, including switching
to python3.
Usage of _static_ files (dropins) to override some of autostart entries
(enable/disable them in appropriate VM types) is much simpler and less
error prone than automatic generators.
Handling code is implemented in qubes-session-autostart, which is called
from qubes-session.
qubesos/qubes-issues#1151
