Differentiate between Dashboard server and not.

One system is the Dashboard server, while other systems need
puppet-dashboard installed, so they can query the Dashboard server as an
external node classifier.
Move params for dashboard into correct classes.

All parameters which were in puppet::dashboard but are only used
in the new class puppet::dashboard::server have been moved to
that class instead. Spec tests were also refactored to match.
Update format of README for readability.
Merge pull request #22 from ghoneycutt/secure_dashboard

Secure dashboard