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-cycler/package.py

@@ -25,7 +25,7 @@
 from spack import *
 
 
-class PyCycler(Package):
+class PyCycler(PythonPackage):
     """Composable style cycles."""
 
     homepage = "http://matplotlib.org/cycler/"
@@ -33,10 +33,5 @@ class PyCycler(Package):
 
     version('0.10.0', '83dd0df7810e838b59e4dd9fa6e2d198')
 
-    extends('python')
-
     depends_on('py-setuptools', type='build')
     depends_on('py-six',        type=('build', 'run'))
-
-    def install(self, spec, prefix):
-        setup_py('install', '--prefix={0}'.format(prefix))