WIP: New vector interpolations and mappings

[KnutAM]

Implements Hcurl (Nedelec) and Hdiv (RaviartThomas and BrezziDouglasMarini) interpolations and the associated mappings.

To ensure that the infrastructure works well, I would aim to have the following here

• Tests for H(div) and H(curl) on reference element
• Continuity testing for mapped H(div) and H(curl)
• Test homogeneous Dirichlet BC for all interpolations
• Tutorial with H(div) elements: preview
• Tutorial with H(curl) elements preview
• Test reinit without gradients

Possible tutorials/validations

• https://gridap.github.io/Tutorials/dev/pages/t007_darcy/#Tutorial-7:-Darcy-equation-(with-RT)-1
• https://www.dealii.org/current/doxygen/deal.II/step_20.html
• https://fenicsproject.org/olddocs/dolfin/1.4.0/python/demo/documented/mixed-poisson/python/documentation.html
• https://web.pdx.edu/~gjay/pub/MaxwellGoodBadUgly.html
• https://pdfs.semanticscholar.org/e182/9d90751af4d8a3b36e467567136fdaa33b1b.pdf

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 66.50943% with 71 lines in your changes missing coverage. Please review.

Project coverage is 89.79%. Comparing base (5153307) to head (ac0d5ad).
Report is 6 commits behind head on master.

Files with missing lines	Patch %	Lines
src/interpolations.jl	75.00%	33 Missing ⚠️
src/FEValues/BoundaryValues.jl	0.00%	21 Missing ⚠️
src/FEValues/FunctionValues.jl	65.30%	17 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #798      +/-   ##
==========================================
- Coverage   93.57%   89.79%   -3.79%     
==========================================
  Files          39       40       +1     
  Lines        6071     6416     +345     
==========================================
+ Hits         5681     5761      +80     
- Misses        390      655     +265     

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