Tags: add tags and example usage

[sebastiansandqvist]

This is the first component that has had to be stateful. The reason I think that is acceptable is because that state is just the hover state that's used internally in the component.

The alternative would be to have a higher-order component manage that state, but unlike checkboxes where a parent component might care about the checked value, you probably never will care about the hover state.

Some changes from the original Quartz Tag (http://quartz.vhx.tv/js/components) include:

• The label is now required. It used to make the label "Tag" if one was not passed.
• Changed onShow to onClick (thoughts?)
• Changed label_length to maxLength

[sebastiansandqvist]

Jira task VHX-894