UnifiedHighlighter: simplify "maxPassages" input API

The "maxPassages" input to the UnifiedHighlighter can be provided as an array to some of the public methods on UnifiedHighlighter. When it's provided as an array, the index in the array is for the field in a parallel array. I think this is awkward and furthermore it's inconsistent with the way this highlighter customizes things on a by field basis. Instead, the parameter can be a simple int default (not an array), and then there can be a protected method like getMaxPassageCount(String field that returns an Integer which, when non-null, replaces the default value for this field.

Aside from API simplicity and consistency, this will also remove some annoying parallel array sorting going on.