More first-order CR type elements

[termi-official]

These are basically useful to check if we got all assumptions right. Towards #558 .

TODOs

• Add citations to documenter
• Investigate what is going wrong

[codecov]

Codecov Report

Attention: Patch coverage is 98.14815% with 1 line in your changes missing coverage. Please review.

Project coverage is 93.20%. Comparing base (6228782) to head (64c591d).
Report is 2 commits behind head on master.

Files	Patch %	Lines
src/interpolations.jl	98.07%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #838      +/-   ##
==========================================
+ Coverage   92.94%   93.20%   +0.26%     
==========================================
  Files          38       38              
  Lines        5756     5816      +60     
==========================================
+ Hits         5350     5421      +71     
+ Misses        406      395      -11     

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[termi-official]

Finally found some time to fix this and found another minor bug in the wedge integration rule. It should give us some prospective confidence in the dof management and interpolation API to also be able to support non-trivial element types. I could not find CR types for pyramids and wedges tho.