More profile improvements

Some stuff I noticed after a while that were annoying:

• Disables the scrolling behavior for the profile tabs, relevant for qqc2-desktop-style. You will run into this when scrolling down the page.
• Fix the loading state for account model, it should now show the progress bar properly. The loading state is now changed after the pinned posts are loaded too, reducing the apparent layout shift.
• On the topic of the progress bar, it now shows in the correct place and takes into account the list view header height.
• The account tab functionality is now moved into C++ (you can toggle the same filters still exists for future QML usage) which makes it way, way better. No more weird filter behavior!