Added ids and checksums filter
Updated service description with ids and checksums on the GetImages command
Remove starting slashes in case the server url has a dir in it (for instance http://foobar/imbo)
urldecode the complete url before generating the access token
Query params have changed to arrays
Added a helper method for validating local files, and changed some of the parameters for the getImages method
Updated test
Added a method for checking if a local image exists on the server, and updated some of the response mocks to fit the server responses
Added a method for checking if an image identifier exists on the server
Added methods for fetching image data by image identifier and image url