Added the initial support for the database protection with the setuid
mechanism. In the beginning the program creates(or opens) the database
as a special user, and then switches to the real uid and functions
normally.
Finally implemented the permanent permission tables using sqlite3. For
now, performance wasn't a consideration. There are a lot of
optimizations that could be made, like having prepared queries. The code
remains fairly untested.
Now the program is completely functional and is using zenity dialogues.
`sources` directory was renamed to `src`. UI related stuff was moved to
`src/gui/ui`.
