ApplicationPage: Move (un)install & launch to sticky page header

A common problem with this page is that the install button being present in the header is hard to identify for new users, as they expect it to be near the app information.

In order to make it more visible, we take the content at the top of the page (a coloured rectangle with app info) and place the install button there, turning it into a sticky header with two layouts internally for full-height and reduced height. As the user scrolls down, the sticky header shows the reduced height layout and shrinks in height with scrolling down to a minimum height.

In InstallApplicationButton, we take the launch button from the page actions and instead place it next to the install button, as it is highly related to the app.

The sticky header also features a "Scroll to top" button when the user has scrolled down.