Only show IME in navigation bar when it should

Add a flag to indicate that the IME should be shown.  This follows
the continuous ime notification boolean, and if there are multiple
input methods to choose from enabled.  This way the notification
and navigation button show up under the same circumstances (but
not on the same devices).

Change-Id: Ia6a2253061f1876f4bcc511de48c1078e9d96be5