Add `static_panel_nav` option

[darylf]

My project had a requirement to ensure the next/prev arrows don't disappear. We believed this is better for accessibility. I created a new option called static_panel_nav. When set to TRUE, static_panel_nav will always display the next/prev arrows on the screen. The option is FALSE by default, to match pre-existing behaviour of the library.

[darylf]

My Git client also stripped a lot of excess white space.