[FEAT] (extension points scene variables sugar) Now you can get the values of much used variables through the scene or context methods of same name: this.category(), this.series(), this.value(), etc.
Changed the scene variable sugar syntax to follow the results of the made poll.
Two syntaxes:
* a generic one #get(varName, [prop='value']).
* a specific and discoverable one: #getSeries(), #getCategory(), #getValue(), #getSeriesLabel(), #getCategoryLabel(), #getValueLabel(), ... Also for "X", "Y" and "Tick".
Merge branch 'ccc-typical-vars-sugar'