NEURON course exercise sets

[ramcdougal]

18 of the exercise sets from the 2018 NEURON course. The neuron.yale.edu site only has 16 of these. Our extra ones are numbers 9 (inhomogeneous channel distributions) and 11 (the linear circuit builder).

Partial progress toward #1728 and this will resolve #1685

http://nrn.readthedocs.io/en/docs-update/courses/exercises2018.html

[codecov-commenter]

Codecov Report

Merging #1735 (f6fc610) into master (3f2f83d) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1735      +/-   ##
==========================================
+ Coverage   45.45%   45.49%   +0.03%     
==========================================
  Files         550      550              
  Lines      113130   113130              
==========================================
+ Hits        51423    51468      +45     
+ Misses      61707    61662      -45     

Impacted Files	Coverage Δ
src/parallel/bbs.cpp	76.27% <0.00%> (+1.69%)	⬆️
src/parallel/bbssrvmpi.cpp	47.56% <0.00%> (+6.09%)	⬆️
src/parallel/bbsclimpi.cpp	59.19% <0.00%> (+8.62%)	⬆️
src/nrnmpi/bbsmpipack.cpp	92.19% <0.00%> (+10.24%)	⬆️

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[adamjhn]

It's a good copy of the current course exercises on the NEURON website. I've made a few minor suggestions.