Introduce get_main_id() function for TBasePainter
Introduce get_main_id() function for TBasePainter

Simple text id can be required by some external libs (like dabc.js or
go4.js). For such libs text id can be generated. 
Not really required in JSROOT itself
root-project/jsroot,linev/jsroot,bellenot/jsroot,bellenot/jsroot,linev/jsroot,root-project/jsroot,bellenot/jsroot