Merge Sam's work into my fork

Validation test updates

* Remove vestigial #if 0
* Add missing cstring include, std:: in validate.cpp
* Simpler synapse index logic in fvm_cell.hpp

* -S (--syntype) option passes argument through to
  synapse creation in `make_cell`.

* Give synapse mechanisms helpers
* Describe synapses in `cell` with location and param list
* Align exp2syn parameters with nrn generated test
* Add unit tests for exp2syn functionality

* Clean up validation CMake
* Use configure-time path to validation data by default
* Checks in validation data
* Bring validate_synapses up to date with current source API.
* Allow -p option in validation test to point to validation
  data directory.

* Add a tweaked version of exp2syn.mod that is modparser compatible.
* Add option to simple_synapse.py to choose which syn type to use.
* Compatibility tweak for runinng nrn scripts with nrniv -python

Feature/plotting

* Use `units` consistently in miniapp.cpp
* Describe the special treatment of the metadata key
  `label` in tsplot.

* Adds README.md for scripts (currently just for tsplot)
* Renames tsplot.py to just tsplot for simplicity
* Change long option --out to --output for tsplot

* Do not try to plot excluded points if there is no
  excluded time series to plot.
* Perform runtime check on matplotlib version for early
  exit in case of mismatch.

further style fixes in point

* Add -x option to clip extreme y values automatically.

Unicode handling changes between 2.7.9 and 2.7.12, and
what worked transparently in the latter breaks weirdly
in the former. This patch coerces everything to unicode
for great justice.

Fix logger warning issue.

First working implementation.

* miniapp saves more metadata in json output, including units
* tsplot.py will plot multiple timeseries, optionally gathering
  multiple plots on the one axis set

Note that documentation is missing and there isn't a clipping
functionality in tsplot.py, which it should have in the presence
of numerical instability.

added flags for GNU and Intel compilers to the cmake build rules
that generate KNL-specific instructions when the TARGET_KNL cmake
flag is set.

fix cmake to find TBB installed from source

there was a problem with the FindTBB script for cmake where it cmake was
not looking in paths specified by the environment variable LIBRARY_PATH,
which meant that it was not finding the TBB library files when TBB had
been installed from source and configured with tbbvars.sh

Address gcc 6.1 warnings

add missing cmath header

GCC 6.1 was unable to find cmath in src/point.hpp

Feature/refactor tests directory

Adapt sources to include test_unit.hpp
Add empty CMakeLists.txt to all test type directories

Gtest is currently copy twice!

Fix optional<X&> assignment.

* Correct implementation of operator=().
* Unit test for optional reference assignment.

Modifications to util::optional for KNL compilation