For mercs: all now have [liberal] hire triggers

Mercenaries w/o hire triggers (default) were no longer deterministically being hireable.  Some major rulers were limited to 5 or fewer total merc companies that they could hire. We know that this wasn't previously the case before Charlemagne, so we've now forced the merc hire triggers to be open instead of relying upon whatever the default behavior is.  We did this for consistency where there *were* hire triggers too, except when they were obviously a plausibility issue.