install: separate scripts for configuration update and image update
install: replace installation scripts with a DBus-activatable service
install: restore the old call interface: puavo-update-client
Whitespace cleanup
install: return or raise the output of update commands

Update scripts do not exit with an error value if the fail, they just
print error messages. This commit make puavo-client-daemon to report all
the output back to the caller.

BUT, all update scripts should be fixed to fail if they fail. For
example puavo-install-and-update-ltspimages does not fail if it fails to
fetch files..
install: emit dbus signal when an update is available
install: add updater indicator applet

The applet communicates with the client daemon using DBus. Applet is
written in Python because it has appindicator API, Ruby does not seem to
have one.
Tabify Makefile
install: add XDG autostart file for update applet
Merge branch 'update-service' into trusty

This branch moves the responsibility of downloading andinstalling image
and configuration updates from puavo-update-client.conf upstart script
to a dbus-controllable and activatable daemon process.

The change is required because personally administered laptops might
have automatic updates disabled and hence there can be more than one way
to trigger the update. DBus provides a great medium to transferboth
events and commands.

A simple indicator applet is provided to meet the minimum requirements
of user triggerable updates.

The old update script, puavo-update-client, has been changed to call the
daemon via DBus instead of calling update commands on its own. It is the
daemon which controls the download and install logic which now lives in
/usr/lib/puavo-install-client.

Image downloading and installing procdures stay untouched, this branch
only changes how updates are triggered. However,
/usr/lib/puavo-ltsp-install/update-images needs to be fixed to exit with
non-zero status on failure. Currently, it is almost impossible to report
update errors back to users.