Extend createStyle so it can create external stylesheet references instead of inline styles

[timomayer]

Is your feature request related to a problem? Please describe.
Inline styles give great performance when it comes to loading one single page. on a website with many sites it is a problem because css code can not be cached when component is loaded once and profit from improve load time (because of caching) on every next occurance of the component.
insead every html file is quite big (because it contains all inline styles) and every style has to be loaded again and again.

Describe the solution you'd like
make it possible in bio-element to instead render all styles inline load them via @import ...