make bindings use static version of protobuf to allow easy usage in node

[MoKob]

Using static libs for protobuf via mason is allowing a problem-free installation of our node bindings via npm. It comes at a price, though.

There is a heavy interaction between system includes and local includes, which seems to be confusing cmake a lot. I had to remove the link to /usr/local/include for osx builds, since the inclusion kept resulting in conflicting definitions between the system wide include path and the mason dependency (see https://github.com/Project-OSRM/node-osrm/issues/212 for reference).

[codecov-io]

Codecov Report

Merging #151 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #151   +/-   ##
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  Coverage   96.18%   96.18%           
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  Files         127      127           
  Lines        2803     2803           
  Branches      224      224           
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  Hits         2696     2696           
  Misses         22       22           
  Partials       85       85