Remove export of ScalarValues and VectorValues

[KnutAM]

ScalarValues and VectorValues are exported but don't seem to be defined.
I also added a test to check that no symbols are exported that haven't been defined. Not sure where to put this test though...

[fredrikekre]

Removed in #404. Docs look more ugly now, it was nice to be able to reference both CellVectorValues and FaceVectorValues as VectorValues:P

[KnutAM]

Not sure why "curl" fails, the new test passes when I run ]test on my computer
Edit: I'll improve the test to solve this, seems to be an issue with qualified use...

[kimauth]

We could document the VectorValued and ScalarValued Traits and refer to them in the docs instead. Though the question is where in the docs that should go, it's not really supposed to be exposed to the user.

Not sure if I like writing out CellScalarValues and FaceScalarValues everywhere, e.g. PointScalarValues uses some of these functions as well. That list easily becomes lengthy.

[codecov-commenter]

Codecov Report

Merging #416 (1198c06) into master (fb4e1f1) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #416   +/-   ##
=======================================
  Coverage   91.05%   91.06%           
=======================================
  Files          22       22           
  Lines        2897     2898    +1     
=======================================
+ Hits         2638     2639    +1     
  Misses        259      259           

Impacted Files	Coverage Δ
src/Dofs/ConstraintHandler.jl	93.47% <0.00%> (+0.02%)	⬆️

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[KnutAM]

Could one write e.g "where u is VectorValued" where the link is to a page documenting what VectorValued means (but not giving this page in the menu). And also documenting ScalarValued on that page?

[kimauth]

Seems not so nice to me to hide it away like that. Perhaps just an introductory section at the top of https://ferrite-fem.github.io/Ferrite.jl/stable/reference/fevalues/ which explains that there are ScalarValues and VectorValues, where the VectorValues are zero-padded versions of the ScalarValues? I remember that I found this hard to understand in the beginning.

[KnutAM]

Yes, that would be even better!
Note that as far as I could find, this "problem" only occurred in the two places where I changed it.
Should that intro be done in this PR? (I'm probably not the right person at this time to write it...)

[kimauth]

No need to do it in this PR, the PR is after all about removing the export that I forgot to remove in #404 . I can draft something for the VectorValues and ScalarValues.