AdTypeDefinition Tool: Utility for building AdTypeDefinition JSON
 * Change AdTypeDefinition & CdnMapping property setters to internal
 * Add assembly InternalsVisibleTo attribute to DeliveryNetworkUtilities for BuildAdTypeDefinition
 * Add FileInfo extensions for Reading, Writing and Appending text with a single call
Traveltorial: Change AdTypeDefinition CDN mappings to have FileName property reference instead of extension and mime-type
Merge branch 'CdnMappings'
Merge branch 'AdTypeDefinitionTool'