Iftach Sadeh / ctools

…new refitting logic, and revert back to original reference values for the unit tests

The "refit_if_failed" parameter instructs ctlike to perform a refit in case of a fit failure. Fit failures are either a stalled fit, an exhaustion of the number of iterations, or a significant difference between the number of observed and predicted events.

All likelihood ctools now derive from the ctlikelihood base class. This avoids code duplication and provides all likelihood tools with a uniform interface.

(still need to remove some debug statements later)

…served events in ctlike.