Fix issue #7296314, issue #7296314.

7296314 Crashing dreams are stuck
7296510 Transition from lock screen to dreaming is really bad

The window layer for dreams is now moved down below the keyguard,
so that some of the expected stuff like crash and ANR dialogs can
be seen on top of them.  While doing this, I reorganized how we
define the layers so the constants are just in the switch statement,
so it is much less crazy-making trying to read how things go
together.

We now have some special cases for when a dream is being shown
to turn off its animation if the keyguard is currently shown.
Since we know it will be hiding the keyguard we need it to be
shown immediately so that you don't see whatever is behind it.

Cleaned up some handling of when the lock screen is displayed
while a FLAG_SHOW_WHEN_LOCKED window is displayed, so that the
lockscreen doesn't transiently get shown and mess up the fullscreen
or system UI state.  This also fixes problems with any normal
activity that is doing this.

Hid the methods on DreamService for setting lights out mode.  It
doesn't make sense to have such methods on DreamService, because
you can just as well do that on your own View that is showing the
dream content, and when you can do that you can fully participate
in the (required) interactions about it such as being told when
the mode goes away.

The DreamService method for going fullscreen now uses the window
flag for doing this, which is what you want, because you want this
state to persistent on that window and not get knocked out if
something above the window tickles the system UI state.

Also fixed the problem where dreams that hid the status bar would
have a jerky animation when going away, since they were causing the
activity behind them to be layed out without the lock screen.  This
is a kind-of ugly special case in the window manager right now to
just not layout windows that are behind a dream.  Good enough for MR1.

Change-Id: Ied2ab86ae068b1db0ff5973882f6d17b515edbcd