Added the removeIllegalChars() method to hierarchyBuilder.py that helped
to prevent the issue ("_injury" parent) in one of the main test sets.

The removeIllegalChars() method was implemented to avoid the need to
hard-code in the specific characters to replace. Fixed the issue where
"poison / injury" was being changed into "_injury". Makes the code more
readable and mutable.
Changed the name of the default input CUI file and default Top Hierarchy file