Adding the possibility to have a configuration file

[tatintart]

I didn't want to have to stash my own configuration for every change.

The config file is loaded as a bash file, and can contain values for the existing configurable properties:

• snapshot_interval_seconds
• snapshots_per_second
• keep_video_days
• videos_location (one level below the "captures" folder)

And an additional show_config variable which triggers, if set to something different than 0, the display of a summary of the configuration values.