More config file options.

[andrew-2e128]

Added db_path to config file, needed mostly for packaging.

Here are some notes/tasks (I will do later) to make it easier to configure and package dim.

• ffmpeg & ffprope paths should get their own options, but maybe with smarter defaults (searching PATH).
• Logs path should get it's own option. DONE
• All uses of ffpath should be generally reworked as usually the binary is in read-only directory. (should backward compatibility be considered?)