Improve index updating performance

[ayebear]

When an index gets large (say 100 queries), this means that adding/removing components from entities becomes 100 times slower. Structure the index like a tree - sort the components, but use the first component as the top level of the tree, and go deeper to find all the components. The only trade-off here is large queries with many components will have to go deeper in the tree, but that's not a big deal.

Edit: This won't actually work as-is, but may require other designing/data structures.