Controlgroup should have theme property

[gabrielschulhof]

@gnarf37 was complaining that the theme needs to be set on each child of a controlgroup individually instead of it being possible to set the theme on the controlgroup itself, and have each child inherit the theme from the controlgroup.

[gnarf]

To be honest, having any arbitrary parent accept a data-theme or data-content-theme would be useful too.

[jaspermdegroot]

+1

[jaspermdegroot]

@gabrielschulhof - Shall we try to add this for 1.3 together with changing controlgroup into a widget?

[jaspermdegroot]

Changed the milestone to 1.4 because it's not easy to implement. We are planning on looking theme inheritance for 1.4 so this is not something we will land in 1.3.

[ryanilg]

+1 Would be super useful!

[mrextreme]

+1