Refactor AbstractapplicationHeader with a new "ScrollIntention" concept

ColumnView which is the main thing used as parent for pages (and the c++ entry point we can have) already filters child events, expose a "scrollIntention" signal on the attached property, which can be like mouse events be intercepted and in the signal handler set accepted to true, which will block further propagation. so we can resize the heading without any events arriving to the flickable and starting to forward only when the header slide is complete. either open or close. vokoscreen-2020-11-26_11-51-57