Nestpy

Some quick fixes for the pypi package which should allow users to build from scratch should the binaries not compile.
Also have synced to NEST v2.2.0 to include full features in the new version.

Fixes bugs in the pypi install for linux users, fixes dependencies for manylinux build.

**See nest v2.1.2 for full physics features. **

If on linux, run `pip install git+https://github.com/NESTCollaboration/nestpy.git`
as we are missing a quick fix in setup. This will be fixed in the next release. Thank you!

Significant function changes:
* testNEST --> execNEST (renamed function)
* Vectorized yields functions in helpers module (for fast python implementation)

New nestpy features:
* New free parameters registered
* Cases of void initialization in tests fixed
* Introduced files for debugging tests as we improve code
* Prepared for NEST v.2.2 release.
* Solved half of GetS1 and GetS2 issues opened in 37

- Main change is in changing all testNEST to execNEST functions which better describe its functionality.
- Slightly better functionality: position is now 3 arguments vs. 1.