SwitchBasemapSample created

- Created a sample to switch base maps for a web map using -
openIntoMapView:withAlternateBaseMap:.
- Just need to test a few scenarios before creating a pull request
not using any of these images
Updated the folder and group names
Added placeholder images; shadow on collection view cell
worked on the suggestions in the comments
method name changes and added method descriptions
a common delegate
made changes as per comments

- common delegate for both list and collection
- changed method names in helper class
- caching basemaps
- list view cell no longer highlighted
- changed button item titles to List and Grid
- fixed the zoom problem (now maintains the zoom scale)
- sending back the basemap now instead of the web map
- added comments on methods explaining their function
Merge pull request #59 from Esri/new_SwitchBasemapSample_gagan

Created a sample for switching basemaps