Added support for un-highlighting nodes via attributes.
Added support for un-highlighting nodes via attributes.

Fixes problem 2 in EmmittJ/PoESkillTree
#96.

Note that you won't be able to un-highlight a right-clicked attribute if
you spec out of it after highlighting it. Is this really an issue
though?

PoESkillTree/PoESkillTree,mihailim/PoESkillTree,MLanghof/PoESkillTree,BlueManiac/PoESkillTreeSource,nikibobi/PoESkillTree,brather1ng/PoESkillTree,l0g0sys/PoESkillTree,EmmittJ/PoESkillTree,Yskuma/PoESkillTree,Ttxman/PoESkillTree