Added dropbox broadcast notification

To monitor the dropbox an application have to either poll the dropbox
and keep track of all entries or observ the /data/system/dropbox
directory. The later requires that the application runs as system-user.
This commit adds that a broadcast intent is sent when something is written
to the dropbox and an application can just listen on this intent and
then reads the entry with help of the DropboxManager class.
The application have to hold the permission android.permission.READ_LOGS
to get the intent.

Change-Id: I1f77f206a243df69f4ed5306078c47f7bf6181ec