Change the global String Template group structure to welcome highchart in the familiy
Common : html, data, chartbody
LibrarySpecific : imports, charts, graphs
Separating string templates in folders :
	- common
	- 1 per library
In code generation, use of several STgroups
Design of the String template representation of highchart
First highchart visualization : Pie chart
Fix the HighChart data format transformation (it's not JSON, bouh)
Creating a small way to categorize a senML dataset to produce data for the Pie Chart
Finishing the possibility to generate Pie Charts
Handling multiple reduction sequence and choice of the serialization (sorted or not function of the data index type)