Fix #1917: make the view scrollable and keep the share button out of the scrollview

Fix #1917: make the view scrollable and keep the share button out of the scrollview
> This layout appears to be designed to look like a dialog caption, so I think it shouldn't be inside the scroll view (ie: it should remain fixed at the top).

There is not a lot of room in this screen, I'll remove the header and replace the string "Select a blog" by "Select a WordPress site".