Add PythonPackage base class

- Add a PythonPackage class with build system support.
  - Support build phases in PythonPackage
  - Add a custom sanity check for PythonPackages
  - Get rid of nolink dependencies in python packages

- Update spack create to use new PythonPackage class

- Port most of Python packages to new PythonPackage class

- Conducted a massive install and activate of Python packages.
  - Fixed bugs introduced by install and activate.

- Update API docs on PythonPackage

var/spack/repos/builtin/packages/py-phonopy/package.py

@@ -25,7 +25,7 @@
 from spack import *
 
 
-class PyPhonopy(Package):
+class PyPhonopy(PythonPackage):
     """Phonopy is an open source package for phonon
     calculations at harmonic and quasi-harmonic levels."""
     homepage = "http://atztogo.github.io/phonopy/index.html"
@@ -33,11 +33,7 @@ class PyPhonopy(Package):
 
     version('1.10.0', '973ed1bcea46e21b9bf747aab9061ff6')
 
-    extends('python')
     depends_on('py-numpy', type=('build', 'run'))
     depends_on('py-scipy', type=('build', 'run'))
     depends_on('py-matplotlib', type=('build', 'run'))
     depends_on('py-pyyaml', type=('build', 'run'))
-
-    def install(self, spec, prefix):
-        setup_py('install', '--home=%s' % prefix)