This fixes a bug where the system was defaulting to 8 digits max password length.
The UI is best for N <=12, but works for more. I set the default limit to 16 which is
more than most humans can remember. That also seems to be the practical limit for the small
sample of DevicePolicyManagers I checked.
DevicePolicyManagers can always specify more digits if they really want.
Change-Id: I8637e0c9366800886759424b5a28f48dca15c535
This introduces a new activity for changing the password, which takes
care of launching the correct password activity based on the caller's
request and active policy. The security settings activity now uses
this, and it implements the API action for launching the password UI.
