Enhance Joining collector

[amaembo]

The following enhancements could be implemented for Joining collector in future versions:

• Limit length by custom user function (which probably computes the rendered string width in the UI): restrictions on function definition should be clearly specified
• Possibility to cut using custom BreakIterator instance or BreakIterator factory
• Possibility to cut using custom user function which can adapt java.text.BreakIterator or possibly ICU4J BreakIterator
• Possibility to specify the non-default Locale for BreakIterator in cutSymbols/cutWords/maxSymbols modes (need to investigate when Locale differences matter).