This fixes various issues such as:
- missing space in Dart version between the live demo and demo source
links.
- Live example link directing to Plunker for Dart.
The main mixins (`liveExampleLink`*) used to support the generation of
links now assume reasonable default values for their arguments, and in
most cases the defaults are used.
* Dart example links: use http vs https
As agree to with @kwalrath.
6d2d52c588