fix WRITE_SETTINGS to be "dangerous"

(see http://www.fireeye.com/blog/technical/2014/04/occupy_your_icons_silently_on_android.html for an explanation why this is dangerous)

Change-Id: I8f938dc4f528aa2ccbca3d4cec235feb0299c0bd
DocumentsUI: Allow open files instead of URIs

Check files' real path and mime type to open them only in standalone mode.
This allows, for example, installing apks.

Change-Id: I4501c694db84b8595cd3928752254a8914539972