Style methods

@MDCox `svgStyles` methods need to work for both 1) intial population of style dictionary, and 2) population of _style object anytime a style is programatically changed for example [here](https://github.com/GraphAlchemist/Alchemy/pull/381/files#diff-d092630acc3315411e5e19585a122542R82)

Ticketed as #382