Empty callback function is not needed for set()
Add the universal PageHeader component

Backed by PageHeader on Silica and by custom page header component with Controls.
Use the PageHeader component for text in page headers

It looks much better on Sailfish and also moves the custom code to UC
for Controls.
Tweak header heights

Make portrait header height a bit smaller and make landscape header height
depend on back button usage. If the platform does not use a back button,
(such as Sailfish OS), the landscape header height can be smaller.