Safe space at top and bottom updates for mobile

[tracygardner]

Virtual gesture bar and AssistiveTouch virtual home button: Review UX and adapt as needed

Layout is broken on some iOS devices due to use of safe space.

• Change the height calculation for mobile to account for additional UI (issue with ui taller than available space and two finger scrolling)
• Make the whole bottom bar a button
• Make bottom bar height account for safe space
• Position logo based on height
• Adjust for top bar overlay in fullscreen mode from browser on iPad
• Test on a range of devices / sizes
• Test browser (inc fullscreen) and add to home page
• Test portrait and landscape