Added public/private editing

[nkoenig]

Add support for editing models via a PATCH call. I'm limiting the scope of this PR to just the public/private field in models.

[chapulina]

There are conflicts to be resolved

[codecov]

Codecov Report

Merging #67 into ign-fuel-tools4 will decrease coverage by 1.89%.
The diff coverage is 9.30%.

@@                 Coverage Diff                 @@
##           ign-fuel-tools4      #67      +/-   ##
===================================================
- Coverage            78.50%   76.60%   -1.90%     
===================================================
  Files                   16       16              
  Lines                 2214     2278      +64     
===================================================
+ Hits                  1738     1745       +7     
- Misses                 476      533      +57     

Impacted Files	Coverage Δ
include/ignition/fuel_tools/RestClient.hh	100.00% <ø> (ø)
src/RestClient.cc	56.48% <0.00%> (-3.68%)	⬇️
src/Result.cc	90.90% <0.00%> (-9.10%)	⬇️
src/ign.cc	55.15% <0.00%> (-5.72%)	⬇️
src/FuelClient.cc	70.34% <17.64%> (-1.82%)	⬇️
src/ModelIdentifier.cc	92.26% <100.00%> (+0.23%)	⬆️

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[chapulina]

LGTM. The only suggestion I have is documenting the new command on the README and tutorials.

[nkoenig]

Updated tutorial: b4a0925