add .inp (gmsh/CalculiX/Abaqus) support

[marinlauber]

This PR adds the capability to load .inp files, which can be generated by gmsh and are often used with CalculiX/Abaqus.
I've opened a PR in JuliaIO/FileIO.jl to register the new format #JuliaIO/FileIO.jl#414
I've also included some minimal tests and a sample cube file for testing.

Additionally, it fixes two tests in the .obj mesh that were previously failing. I am happy to move this to another PR if you prefer.

[codecov]

Codecov Report

❌ Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.46%. Comparing base (8102339) to head (4d4188d).
⚠️ Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
src/precompile.jl	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #110      +/-   ##
==========================================
+ Coverage   74.82%   75.46%   +0.63%     
==========================================
  Files          10       11       +1     
  Lines         735      758      +23     
==========================================
+ Hits          550      572      +22     
- Misses        185      186       +1     

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[marinlauber]

@SimonDanisch this now works since the ".inp" format has been officially registered in JuliaIO/FileIO.jl#414

[marinlauber]

Thanks!