Slave

Created a serializable Callable to hide the distinction between master and slave. 

The Plugin flow is now:

    CrittercismDysmRecorder :
        Creates serializable UploadRequest 
        Creates callable RemoteRecorder
        Uses Launcher to call RemoteRecorder

   RemoteRecorder:
      Create Crittercism Uploader
      Find dSYM file and add to UploadRequest
      Use CrittercismUploader to upload UploadRequest 

   CrittercismUploader:
      Makes post request to crittercism 
      If error code other than 200, fail build

Added UploadException that will cause the build to fail if the upload fails. 

Allowed absolute dSYM path or relative to workspace path and added Jenkins help for this.