Updating TimingCalibrator, now handles multiple start offsets.

This change was necessary to facilitate the use of n different start
detectors. We will have 4 double sided betas for the ANL 2015 experiment.
In addition, the TimingCalibrator now returns a default calibration if
none is present in the map. This eliminates the need to have the bars
defined in the map if there is no calibration information for them.

Signed-off-by: S.V. Paulauskas <stanpaulauskas@gmail.com>