Allow easy setting editing of height and width properties.
Change names to better reflect property value.
Add white as a preset.
Allow multiple element properties to be added at the same time.
Pull the 'checking for unset colors' code out of prerendering, into the property get() calls, to ensure it can never be unset. (It was possible to get into a state where the controls would try to display a null color/gradient.)
Merge pull request #18 from sall/master

Merge from sall/vixen