Added shadow and border-radius CSS classes

[Blackbaud-SteveBrush]

This will allow external libraries to add SKY-approved drop-shadow and border-radius styles to their elements.

[codecov-io]

Codecov Report

Merging #1571 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1571   +/-   ##
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  Coverage   99.98%   99.98%           
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  Files         391      391           
  Lines        7885     7885           
  Branches     1152     1152           
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  Hits         7884     7884           
  Misses          1        1

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[Blackbaud-ToddRoberts]

I assume the classes are baked into the components, and won't require devs to specify those classes each time they use the component?

[Blackbaud-PaulCrowder]

See my inline comment.

[Blackbaud-PaulCrowder]

I think the CSS class name might need to be something more descriptive of the purpose of the class rather than a particular CSS property it affects. Is there a common use case for rounded borders which we could use for a name? If not, maybe we should go with something like sky-rounded-corners.

[Blackbaud-ToddRoberts]

In theory we use them for active elements (buttons, input fields, etc), in practice that is not consistent.