search results overwritten by previous (unfinished) request

[ashsny]

steps to reproduce:

1. go to search page: https://mavedb.org/#/search (this kicks off a request for everything in the db, which is slow)
2. enter a simple search that will complete quickly in the field (i.e. '5-a') and hit enter

expected behavior

1. your (second) search loads

actual behavior

1. your (second) search loads
2. the first search (for everything) completes and overwrites the results of your second search

[nickzoic]

possibly this becomes less annoying about if VariantEffect/mavedb-api#89 gets fixed.

Otherwise it generally just means cancelling the previous search request when the search changes, so the async response doesn't overwrite whereever we're at.