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