MadGraphControl: fixes and options for MadSpin running
Includes a fix for finding LHE files after running madspin.
Option to revert LHE event weights after madspin modifies them in spinmode=none. See e.g. https://answers.launchpad.net/mg5amcnlo/+question/684169. Disabled by default.
Tagging @zmarshal and @hmildner from an email thread.
Edited by Tadej Novak