Responsive GridLayout

Remove inline CSS from GridLayout to make responsive UIs easier to build.

Extended greatly:

This problem exists for many components which rely on inline style for hgap and/or vgap. It is correlated with an additional issue of poor enforcement of style guides by allowing individual applications to select gaps.

To be able to sensibly allow consuming applications to produce responsive overrides of these legacy layout components we have to remove the inline CSS and reduce selector specificity in the core theme.

Additional note: this is now an urgent requirement of a major consumer.