Second instance of screenlet doesn't obey theme settings of the first one

Normally there should be default theme settings (or default settings for all new screenlets).

There is default settings dialog now, but this only uses couple of window settings, but there could be also some other window settings (window size for example).

Since themes are specific to every individual screenlet, the same solution cannot be used for themes. It would be quite easy to use settings of the first screenlet for default as a temporary workaround for the issue, but there could be also an extra button in every screenlet's settings dialog to save settings of this screenlet as a default for all new screenlet instances.

It should be quite easy to implement.