Tweaks to improve style application performance

[maxkfranz]

Issue type

Feature request

Description of new feature

Make tweaks to the styler in order to improve style application performance, especially at element creation during initialisation.

• Stylesheet.prototype.style() iterates over Object.keys(passedStyleJson) rather than Style.properties.
• Check for mapper updates only to the list of currently-active properties.
• Iterate over existing style properties in the element for element cleaning on applying a new stylesheet, instead of iterating over all possible props.
• Improve performance of style property parsing by using cheap heuristics to avoid regex mapper checks
• Cache default properties without memoize()
• Slightly cheaper checks in ele.isSimple() and ele.isLoop()
• Document how to start from an empty stylesheet
• Refactoring of Selector, esp. w.r.t. matching

Motivation for new feature

Faster init time and faster style changes