Remote update rework

* We can now remotely upgrade Debian packages and not require a reboot

* Likewise with piaware

* A full update will update the kernel, boot files and the like (rpi-update) and reboot

* We now won't accidentally downgrade piaware

* this is probably going to get fancier over time, like giving more control over which version will be installed.
Remote update request improvements

* Fix traceback in request handling

* new function upgrade_dpkg_package

* restart piaware if upgrading it was successful

* new procedure for upgrading dump1090

* restart dump1090 if upgrading it is successful

* add new "restart_piaware" and "restart_dump1090" remote requests

* map newlines and tabs out of uploaded log messages

* new proc fetch_url_as_string

* new proc fetch_url_as_binary_file

* improve version comparing

* comments