Avoid looping behavior with color selection

[henryksloan]

Fixes #304

• Removed watch declarations for swatch colors
• Allow response handler to update frontend colors
  • This was previously handled by the update methods through watch, causing loopy pitfalls
• Refactor frontend color updates to a update_working_colors helper function
• Update frontend color updates when SelectPrimaryColor or SelectSecondaryColor is called

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This change is 

[Keavon]

Excellent! I'm going to try and go through most of our input widgets and update them to use the @update:foo="handlerFunction" approach instead of using watchers, which is clearly a dangerous approach (it gave me hours of troubles with the dropdown menu widget also). Thanks for fixing this.