Add quadratic line element

[TTitscher]

Gmsh node numbering does not always match our numbering, e.g. for quadratic line elements. This changes in the gmsh import allows addressing this.

[codecov[bot]]

Codecov Report

Merging #173 into PDE_reviewed will increase coverage by 0.09%. The diff coverage is 100%.

@@               Coverage Diff                @@
##           PDE_reviewed     #173      +/-   ##
================================================
+ Coverage         80.96%   81.06%   +0.09%     
================================================
  Files               225      225              
  Lines              7276     7297      +21     
================================================
+ Hits               5891     5915      +24     
+ Misses             1385     1382       -3

Impacted Files	Coverage Δ
test/mechanics/mesh/MeshGmsh.cpp	100% <100%> (ø)	:arrow_up:
src/mechanics/mesh/MeshGmsh.cpp	96.88% <100%> (+0.57%)	:arrow_up:
...echanics/interpolation/InterpolationTrussLobatto.h	100% <0%> (+8.69%)	:arrow_up:

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[Psirus]

I'd wait for other interpolations, maybe it happens more often, and it makes sense to introduce a mapping of vector<int> to vector<int> or something that handles it. So that I could say GetGmshToNuToMapping(GmshElementType) or similar.

[TTitscher]

IMO we should handle the whole det(jacobian) thing in a dedicated PR.