Handle tool and pipeline input parsing from JSON where strings can be str or unic

Hi all;
I ran into two issues while getting gkno up and running:

- Parsing JSON inputs provided unicode strings instead of standard ol'
  str strings, so all of the checks that rely on str failed. The
  attached patch generalizes these comparisons to use basestring which
  encompasses both cases.

- Build problems with tabixpp on Ubuntu due to library order. The
  tabixpp head fixes the problem, but that revision is not yet in the
  vcflib submodule dependencies. I don't know enough Git magic to
  submit a pull request with submodules but updating the vcflib
  submodule to the latest tabixpp and then updating the gkno
  dependency will fix it.

Thanks. Looking forward to playing with this more,
Brad