Adds extra null checking when looking up active tree
Adjusted assetsService to deal with weird yepnope behaivior
Add support for looking up 3rd party editor file paths

Adds a file resolver on the mediaHelper, property editors can then
register a resolver to return file paths from whatever format
Changes imagecropper to store config in its property data
Updates yepnope cache in jsinit.cs to append correct rnd value
Ensure that umbracoFile doesnt try to process json as a filepath
Removed crops from umbracoSettings.cfg