Added ability to specify theme information and to update the omnibar after render

[Blackbaud-PaulCrowder]

This supports the eventual release of the theming capabilities of omnibar.

[codecov-io]

Codecov Report

Merging #67 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #67   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          15     15           
  Lines         746    758   +12     
  Branches      124    128    +4     
=====================================
+ Hits          746    758   +12

Impacted Files	Coverage Δ
src/omnibar/omnibar.ts	100% <100%> (ø)	⬆️

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[Blackbaud-TerryHelems]

Could we make BBOmnibarNavigationItemDisplayStyle a bitmask enum instead:

{
  Icon=1,
  Text=2,
  IconAndText=3
}