Added rules for status/nav bar customization when in multi-window mode

Status & nav bars are always visible and opaque when freeform or docked
stack is visible

We still need to refactor the code to allow force opaque to be updated
independently for the status bar and nav. bar. Once that is done, the
status bar should be transcluent if freeform stack is visible and
docked stack isn't and the status bar should be opaque if freeform
& docked stack are both visible.

Bug: 24365214
Change-Id: I48ecc6067c9b0f7239c12c98eb46f3fcefacd4f9