Poor performance on large number of nodes

[jakezatecky]

The tree suffers from poor performance when checking a parent with many nodes. Since those nodes are not necessarily rendered when collapsed, this should not be the case. Likely will be improved with stateless conversion (#12).

[jakezatecky]

Although some recent improvements were made, the performance is still kind of bad on large number of nodes.

[SirGordon]

planning to use https://github.com/bvaughn/react-virtualized?

[jakezatecky]

@SirGordon I am not sure if that applies, as the performance bottleneck here is not on the rendered components per se, but on the computations it takes to traverse children on check state updates and retrievals.

[jakezatecky]

This issue was caused by O(n*n) performance, due to iterating through the checked and expanded arrays for each node. A more optimized version exists that flattens the nodes array and each node now checks against its mapped value.