Add alternative for Tree/Table Multi Select

Multi selection as we know it from SWT is not a feature we want on the mobile clients. This is because such a multi selection simply does not exist.

An alternative on mobile clients is some kind of an "edit mode". This displays a list different e.g. including check boxes, adding delete buttons etc.

I think we should consider to enhance our Tree/Table to be able use some kind of "edit mode" were we can define the buttons, layout etc. Maybe a second row template can be used?