Motivation: Hook scripts for nautilus or other file managers
need to provide the user with feedback that a file is being downloaded.
This commit was sponsored by THM Schoemaker.
Made alerts be able to have multiple buttons, so the alerts about upgrading
can have a button that enables automatic upgrades.
Implemented automatic upgrading when the program file has changed.
Note that when an automatic upgrade happens, the webapp displays an alert
about it for a few minutes, and then closes. This still needs work.
