PRs/issues for stable release with 300 cell examples

[pgleeson]

To ensure 300_pointneurons and 300_cells work across the various implementing packages:

• [x] Sonata branch merged into NetPyNE development https://github.com/Neurosim-lab/netpyne/pull/420 (@salvadord)
• [ ] Merge sonata branch into PyNN master (@apdavison )
• [ ] Record selected cells in 300 detailed network: https://github.com/AllenInstitute/sonata/issues/99 (@kaeldai)
• [x] Minor changes for testing BMTK https://github.com/AllenInstitute/bmtk/pull/73/files (@kaeldai)
• [ ] Issue with dt in BMTK: https://github.com/AllenInstitute/bmtk/issues/75 (@kaeldai)
• [x] Test suite & various example updates/tests: https://github.com/AllenInstitute/sonata/pull/100 (@kaeldai)
• [ ] static_synapse -> nest:static_synapse: https://github.com/AllenInstitute/sonata/issues/102 (@kaeldai)
• [ ] Document Sonata -> NeuroML, add it here https://github.com/AllenInstitute/sonata/issues/97 (@pgleeson)