conditionally add FLAG_ACTIVITY_NEW_TASK when starting page

Subsettings must be started from Activity context, apparently.

Add a flag when it's not started from Activity context. This might not
be catching all cases but should at lesat cover most of them.

Change-Id: I8157ec0cb3d032bb44a0e7dec36637906fc8f1a0
Fixes: 72314527
Test: monkey