Plugin drop-down widgets don't always reflect values in plugin.conf.

[FranciscoCanas]

The behaviour of some plugins' drop-down menu widgets is a bit unintuitive, because the values shown in the drop-downs are only saved when changed:

1. Start with a blank $HOME/.freeseer/profiles/default/plugin.conf file
2. Open configuration tool (ctrl-c) and select recording config page
3. Select Picture-in-Picture from the videomixer drop-down
4. Click 'settings' to open the PIP widget, look at the default values showing for Main and PIP source (for me it's firewire), then close without changing them.

Result: The plugin.conf file has an entry for the pip plugin, but the main and source inputs don't match what the widget drop-downs were showing (as they were not saved).

In order for the pip settings to be saved to file, user would have to modify them first.

Two ways to address:

• We can add a callback to save settings when the user closes a plugin's widget, which ensures that whatever settings were showing in the drop-down get written to file.
• We will have to rework the default values that get saved to the plugin.conf file for each of the affected plugins so that they match the initial values shown in their drop-down menus.

Plugins affected (may depend on what devices are available on your system): PIP, multiple audio inputs, Pulse Audio Source.