Making CN Pre-Content Handler Aware

There's not much in CentralNotice that actually depends on Content
Handler (introduced 1.21) so I went in and re-added the legacy stuff.
Therefore master should work on 1.20 and probably 1.19.

Change-Id: I9db7c7b83611f1913a4a9eb3bdc3b26417a38cf4
Merge "Making CN Pre-Content Handler Aware"