Button theme

[smhigley]

Type: feature

The following has been addressed in the PR:

• There is a related issue
• All code matches the style guide
• Unit or Functional tests are included in the PR

Description:

Adds button theme, including down arrow icon to Button

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@40facca). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master     #251   +/-   ##
=========================================
  Coverage          ?   98.95%           
=========================================
  Files             ?       24           
  Lines             ?     1431           
  Branches          ?      414           
=========================================
  Hits              ?     1416           
  Misses            ?        0           
  Partials          ?       15

Impacted Files	Coverage Δ
src/button/Button.ts	100% <100%> (ø)

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