Split Overview page from app grid

This change introduces following improvements:

• Separate page for running activities to give them more space and visibility.
• Button on left side of home bar to activate overview page.
• OSK button is always visible, it may be needed for control OSK for app search when home unfolded.
• Activities use maximum 70% of screen width to allow get visible neighbor activities.
• Centered preview and rounded corners of activity (maybe also need to limit drag area only to thumbnail area).
• Activated activity moves to end of carousel and carousel scrolled to to previous one. Allows access most recent open apps first.
• Disable fold when new activity added (when user launched app and then unfold home again before activity launched)
• Disable scroll on activity activation when overview unfolded to not disrupt user's scrolling progress.

It is alternative change like !1079 but more android-like with separate button to open activities list Grabbed multitasking image from there.

Known issues:

• HdyCarousel doesn't support different-size pages, so each activity takes widest size.
• When OSK enabled, some windows flaps win size, so update thumbnail disabled for this.
• After rotation sometimes for some windows thumbnail has wrong size, it seems because request_thumbnail runs before window finished.