Herwig7_i: Add option to turn off shower scale variation
We add a very simple option to turn off the shower scale variations for internal matrix element processes. These variations are turned on by default and this option allows for them to be turned off.
This is neccessary since a lot of known warnings will be printed out in some cases and with turning off the shoer scale variations the problem of huge logfiles can be mitigated quite a lot.
The changes have been tested with a JO that strugeled with huge logfiles.