* Config option for global default dashboard
Add config option to set a global default dashbord. This will be used
instead of the user's "Default" dashboard unless they have changed their
default dashboard in their user settings.
* Use a dropdown for the default_dashboard option
Update generate_dynamic_config_panel to allow assoc arrays with
`'value'` and `'description'` as keys and change to a select box.
* Fix PHP style issues lost during merge
