Clean up

[Rombur]

• Use new deal.II functionality
• Fix typos
• Prefix private variables with an underscore (up to now, that was only partially done)
• Replace BOOST_FOREACH by a regular for loop

[codecov-io]

Codecov Report

Merging #257 into master will increase coverage by <.01%. The diff coverage is 99.09%.

@@            Coverage Diff             @@
##           master     #257      +/-   ##
==========================================
+ Coverage   94.99%   94.99%   +<.01%     
==========================================
  Files          72       72              
  Lines        5115     5116       +1     
==========================================
+ Hits         4859     4860       +1     
  Misses        256      256

Impacted Files	Coverage Δ
cpp/source/deal.II/post_processor.h	90% <ø> (ø)	:arrow_up:
cpp/source/deal.II/electrochemical_physics.h	100% <ø> (ø)	:arrow_up:
cpp/source/deal.II/supercapacitor.h	100% <ø> (ø)	:arrow_up:
cpp/source/utils.templates.h	100% <100%> (ø)	:arrow_up:
...source/deal.II/electrochemical_physics.templates.h	98.62% <100%> (ø)	:arrow_up:
cpp/source/deal.II/post_processor.templates.h	99.59% <100%> (ø)	:arrow_up:
cpp/source/deal.II/supercapacitor.templates.h	85.21% <98.79%> (+0.05%)	:arrow_up: