This PR implements parameter auto-scaling before fitting to address the issue reported in #1531 and is one of the solutions discussed there.
It should no longer be necessary to call
Also: Please update to iminuit 1.3.2 that @HDembinski released today: http://iminuit.readthedocs.io/en/latest/changelog.html#august-5-2018
In the few fits that we run have automated in Gammapy: they now all work without
Please report any issues you find soon, the Gammapy v0.8 release is planned for Monday!