Computed styles do not show important properties

[bhackett1024]

Computed styles in the devtools do not show whether the style is important. Computed style information is rendered by DeclarationValue components. The state passed into DeclarationValue comes from the MatchedSelector component which created it. The state passed into MatchedSelector comes from createComputedProperties. The ComputedProperty objects which createComputedProperty reads from already have a "priority" property that will be "important" for properties that come from important styles.

Fixing this requires the following changes:

DeclarationValue needs properties indicating whether the associated selector is important.
DeclarationValue needs to render the priority indicator when set.
MatchedSelector needs properties indicating whether the selector is important. Putting this in MatchedSelectorState reduces plumbing requirements.
MatchedSelector needs to pass in priority info to DeclarationValues they create.
createComputedProperties needs to set the priority indicator on MatchedSelectorStates it creates, by reading from "property.priority"