Uses a lockfile.

To determine if a process is already running.
The lock is released when the main process dies, so it should fixes issues when relaunching gtorrent after a crash.
Implemented some more setting, restaured an accidentally deleted method
Implemented the last settings, now require testing.
Fixed a bug with the lock file.

The lock was created in a place requiring high permissions, resulting in potentially incorrect behaviour of the program.
Removed some useless debug lines
Merge pull request #78 from gtorrent/wip/use-settings

Implement settings.
Update addmagnet.sh
Fixes the issue where gtorrent.lock is checked for even if the directory
doesn't exist.