Make NAVIGATION and FONT into classes.

- Recognize that NAVIGATION_set_default_configuration() should really
  be the constructor for NAVIGATIONCONFIGURATION and then implement it
  that way.
- Recognize that NAVIGATION::build(OBJ *, unsigned int) should really
  be implemented as NAVIGATION::build(&objmesh).  Once again "parent"
  shows its worth.
- Where appropriate change while loops to for loops.
- Where appropriate change "unsigned char" to "bool"/"const bool".
- Notice (and fix) that FONT::load() is missing the return status for
  when it's successful, i.e., before it always returned false even when
  it worked.
- Debated about deleting "filename" parameter from FONT::load() method.
  Decided that there might be some cases where the "filename" is
  different from this->name.