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[bot]]

Codecov Report

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

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

```diff @@ 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](https://app.codecov.io/gh/JuliaApproximation/ApproxFunBase.jl/pull/595?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation) | Coverage Δ | | |---|---|---| | [src/Spaces/ConstantSpace.jl](https://app.codecov.io/gh/JuliaApproximation/ApproxFunBase.jl/pull/595?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL1NwYWNlcy9Db25zdGFudFNwYWNlLmps) | `57.26% <50.00%> (-0.13%)` | :arrow_down: | ... and [26 files with indirect coverage changes](https://app.codecov.io/gh/JuliaApproximation/ApproxFunBase.jl/pull/595/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation)

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[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!