Lots of changes to RichardsBorehole, and minor changes to the tests.  This addresses issue #2750 .  Changes include: character is a function; well_constant added to user interface; auxvars added so RichardMaterial values do not need to be used; better algorithm for eigenvalues/vectors ; contribution behind and ahead-of is now better for boreholes with lots of points; and fixing some tabs and banned keywords.  Also implemented suggestions from Andrew S.
Fixing documentation with Refs #2758
Merge pull request #2759 from joshua-cogliati-inl/feature_2758

Fixing documentation with Refs #2758
Merge pull request #2752 from WilkAndy/feature_2750

Lots of changes to RichardsBorehole, and minor changes to the tests.  Th...
Merge commit '0109985e4a51ec453d777554f629f675940d5e9f'