Refining layout and navigation

Improves:

• layout to always be full screen with no page scrolling
• on mobile it's full screen but with the header and footer out of view to maximize space
• keeps "next" and"previous" buttons on all chapters but uses disabled property to turn them on and off to the user
• uses the button component for all the buttons, and adds a prop to change the color
• adds "go to start" and "go to end" buttons and attempts to position them. this needs work, but they function correctly.
• adds the references section to the end. this needs to be worked on so all references can appear - possibly in place of the image or over theimage