Ensure node searching is handled well for large trees

[gibsramen]

Came up in this morning's (09/01/2020) meeting.

When there are a lot of tips in a tree (i.e. EMP with 300k), the search box auto-suggestion can be very slow. For example if the node names are the sequences (TACGTCA...), searching for "TAC" takes a long time as there are potentially many nodes to be suggested.

@kwcantrell had the idea of maybe showing only the top N hits. Alternatively we could make the auto-suggestion functionality optional for users who are visualizing large trees.