applets/kicker: move Return handler from abstract to grid delegate (6.6 only)

We need slightly different behavior in the different delegates. In 6.7, we have better solution for this, but in 6.6.5 we end up with two onReturnPressed handlers activating, as both the abstract delegate and the list delegate have one. The sidebar delegates do their own thing anyway, so we can just move the extra handler to the only one that does not have an explicit keys handler yet, the grid delegate.

BUG: 521001 FIXED-IN: 6.6.6