Moves Treemap's tooltip message to a function overridable in the context.
Moves Treemap's tooltip message to a function overridable in the context.

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