Restart backintime

There's a directory "~/.local/share/backintime" where backintime keeps its information.  Specifically, the worker.lock contains the PID of the process; "kill `cat ~/.local/share/backintime/worker.lock`" stop the currently-running process. The "worker.message" file contain the message displayed in the tray notifier or backintime-gnome, and the "takesnapshot_.log" contains lots of good debugging messages if needed.