Add Image Service to Basemap Gallery

[justingreco]

Include option to view historic imagery in basemap widget. The current year can be accessed through Esri imagery basemap on main list.

• [x] Add tab to toggle between maps and imagery
• [ ] Change color of property lines to white when imagery or a darker map is selected
• [x] Filter imagery years based on if map extent intersects Raleigh imagery boundaries
• [x] Switch to latest countywide imagery when users go outside Raleigh
• [x] Warn users when they go outside Raleigh and the imagery changes