Add historic maps

[apjmason]

Historic map feature enhancement including the following steps

• Add georeferenced layers from allmaps to base map
• Add ability to toggle map layers on and off
• Add ability to associate item locations with specific historical maps
• Add contextual button to walking tour pop up to load map view and close popup
• Experiment with adding image in popup with zoomable abilities, a la Carl Clubs / Cleveland Historical

Use this georeferenced image for testing allmaps reverse positioning abilities.