[bubblechart][m] Use a dedicated object to store/lookup nodes for each level
[bubblechart][m] Use a dedicated object to store/lookup nodes for each level

+ small indentation/scope fixes

RCGTDev/openspendingjs,openspending/openspendingjs,openspending/openspendingjs,openspending/openspendingjs,openspending/openspendingjs-old,RCGTDev/openspendingjs,openspending/openspendingjs-old,openspending/openspendingjs-old,RCGTDev/openspendingjs,openspending/openspendingjs,RCGTDev/openspendingjs,openspending/openspendingjs-old