Add ability to specify modal size of small, medium, or large.

[Blackbaud-AdamHickey]

Adding small, medium, and large configurations for the modal. #489

[codecov-io]

Codecov Report

Merging #767 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #767      +/-   ##
==========================================
+ Coverage   99.94%   99.94%   +<.01%     
==========================================
  Files         286      286              
  Lines        5136     5145       +9     
  Branches      598      602       +4     
==========================================
+ Hits         5133     5142       +9     
  Misses          3        3

Impacted Files	Coverage Δ
src/modules/modal/modal.service.ts	100% <100%> (ø)	⬆️
src/modules/modal/modal-configuration.ts	100% <100%> (ø)	⬆️
src/modules/modal/modal.component.ts	100% <100%> (ø)	⬆️

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[Blackbaud-PatrickOFriel]

Looks good pending @Blackbaud-ToddRoberts review

[Blackbaud-ToddRoberts]

Looks good to me. Which team did the request come from? I want to see if their designer has guidelines for when to use which size.