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.