Icon and Menu fixes

[tedbarnett]

Let's clean up the icons and menus a bit (though will still be messy for now):

• Add an icon for "map markup" (with a pencil icon?). When tapped it toggles the menu bar at the bottom of the screen (with the colored draw icons) on/off. Defaults to off when app loads.
• add an icon for "overlay map" (icon of a map?). When tapped, it pops out the list of overlay maps ("Castello - 1660", etc.). Add a new map option called "None" that hides the overlay map.
• delete the "Map Overlay" menu item we have now (since icon/button above replaces it)

[tedbarnett]

Nice to see the map icons. Great idea!