Improve keyboard accessibility

[patudom]

• see if date time can be organized into columns instead of rows so tabbing goes between up & down for each element rather than across up for all elements, then down for all elements.
• checkboxes need clearer focus styling. (It's possible I made the boxes larger without also increasing the size of the focus bubble, so it's being hidden).
• icon-buttons (and all buttons in general) need clear "focus" + "active" combinations (focus & active; focus & not active; not focus & active; not focus & not active).
• credit-logos should not appear in the tab sequence before the play/pause and date picker.
• Splashscreen content should be tab accessible, and content behind the splashscreen should not be accessible until the tab is closed.
• When info book panel is open, everything on the canvas behind the book should still be tab accessible.
• Rearrange top divs so tab order goes from book to location button to checkboxes.