Implement calculus operations for ConstantSpace

[LucasAschenbach]

I have implemented the integrate and differentiate methods for ConstantSpace. This addition was motivated to add support for taking the norm of ConstantSpace functionals. I have also added a test for the norm operation.

[codecov]

Codecov Report

Patch coverage: 50.00% and project coverage change: +0.31% 🎉

Comparison is base (6080984) 74.36% compared to head (e5be1eb) 74.68%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #595      +/-   ##
==========================================
+ Coverage   74.36%   74.68%   +0.31%     
==========================================
  Files          80       80              
  Lines        8418     8421       +3     
==========================================
+ Hits         6260     6289      +29     
+ Misses       2158     2132      -26     

Files Changed	Coverage Δ
src/Spaces/ConstantSpace.jl	57.26% <50.00%> (-0.13%)	⬇️

... and 26 files with indirect coverage changes

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[jishnub]

I think the test for the integral needs to be added to ApproxFunOrthogonalPolynomials, as that requires Chebyshev to be defined. In this PR, let's just remove the norm test for now. Perhaps a test for the derivative may be added

[LucasAschenbach]

Got it, thanks for the review! Should I create a PR for ApproxFunOrthogonalPolynomials?

[jishnub]

Sure, but that test PR would need this to be merged first. Maybe you can bump the patch version of this package to 0.9.15 in this PR, and set the minimum compat bound for ApproxFunBase to 0.9.15 in the PR to ApproxFunOrthogonalPolynomials

[jishnub]

Thanks!