Issue #6:  Allow whos_online IP to be blocked

Update the whos_online script to display a link to allow the associated
IP address to be added to the blocked IP list.
Issue #5 and #6:  Function updates

Updates to provide functions used by the whos_online script to add a
single IP address to the blocked IP address list.  Additional function
changes to provide IP address consolidation and to use better naming for
the function input/output variables.
Issue #5:  Simplify the admin interface

Restructure based on function interface changes.
Issue #5 and #6:  Readme updates

Update the readme to reflect the plugin's current admin-page layout and
to describe the integration with the whos_online script.