Fixing non-scrolling of workspace view after opening/closing AllApps vew.

The reason for non-scrolling was excluding the pages view from the
accessibility hierarchy by marking it as non-important. So, I just
removed the code manipulating [non]importance of the PagedView.

However, this would make the PagesView accessibility-focusable, which is
undesirable. It becomes focusable because it supports long clicks in "normal"
mode. Since it doesn't support accessibility long clicks (i.e. Overview mode is
fetched NOT via accessibility long-click), I just disabled accessibility
long-clickability, which made PageView non-focusable, and it started to behave
correctly.

Bug: 21281859
Change-Id: I7ab01e5f39cb37c456c961199c27458c9bda1c3d