Merge pull request #167 from jwj61/master

Updating contributors
Fix name of Dartmouth
For abelian fields, only compute character group if the conductor is small enough or the page may take too long/time out.
For a quadratic field, compute its Dirichlet character directly for speed.
Use conductor cutoff for computing Dirichlet characters of quadratic fields.  We can compute the characters, but the links would be useless.