Improve configuration: add 'align' and 'priority', and switch to actual objects

[cerlestes]

These changes will allow users to configure a default alignment and priority for all added shortcut buttons, and also allow them to override those settings per shortcut by switching from a comma-separated string configuration to actual, extendable objects.

The change is non-breaking, as the introduced settings will fall back to the same behaviour, and the old string-setting parser is left intact.

Please change the added code as desired.