adds LFPy@2.2.3

This PR adds the LFPy Python package.

packages/py-lfpy/package.py

+from spack import *
+
+
+class PyLFPy(PythonPackage):
+    """A Python package for calculating extracellular electric and magnetic
+    signals of neural activity from multicompartment neuron models.
+    """
+
+    homepage = 'https://LFPy.readthedocs.io'
+    pypi = "LFPy/LFPy-2.2.3.tar.gz"
+    git = 'https://github.com/LFPy/LFPy.git'
+
+    maintainers = ['espenhgn']
+
+    version('2.2.3', sha256='fc0a3b784621d27cffabe4b6bcc13724f338c1dd')
+
+    depends_on('python@3.6:', type=('build', 'run'))
+    depends_on('py-pip', type='build')
+    depends_on('py-h5py', type=('build', 'run'))
+    depends_on('py-matplotlib', type=('build', 'run'))
+    depends_on('py-mpi4py', type=('build', 'run'))
+    depends_on('py-numpy', type=('build', 'run'))
+    depends_on('py-scipy', type=('build', 'run'))
+    depends_on('py-setuptools', type=('build', 'run'))
+    depends_on('py-cython', type=('build', 'run'))
+    depends_on('neuron@7.7.2:', type=('build', 'run'))
+    depends_on('py-lfpykit@0.3:', type=('build', 'run'))
+    depends_on('py-pytest', type='test')