Updated installer YAML settings file.

Replaced debugVerbosity with enableDebugLogging.
Content refresh improvements.

Closes #259.
* On-focus refresh now listens to window event instead of checking for
state change every 0.5s.
* Added setting to enable/disable on-focus refresh.
* Added File menu item to manually refresh content.
* Old settings files get updated when parsed.
* The installer settings file has been updated.
* Swapped the masterlist update icon to a download icon, as it's more
suitable.