No integral flux UL capabilities

[samanthalwong]

Integral flux is calculated in write_validation_info in rbm.py by integrating the SpectralModel from either a RE or FoV background analysis. gammapy's SpectralModel.integral_error returns the integral flux from the model but has no UL handling. Since the lightcurve tools behave badly for calculating integral flux, I believe this needs to be manually implemented (unless anyone knows of a better way to do this!).

[steob92]

Gammapy Parameter allow for profile likelihood scans, this is how upper limits and asymmetric errors are calculated. I'm not 100% sure of the implementations but you can specify the min/max of the scan and the number of scan points. Maybe looking at the Fit class to see how the calculation is done. With the likelihood profile we can get the upper limit by hand.