Filter for un-mutated bases

[emmahodcroft]

It's very cool that one can use the filter to look for sequences which have a particular AA or nuc change, but it would also be cool to filter for sequences that don't have the change - particularly useful if you have a bunch of sequences with the mutation and want to find the few exceptions.

For example, for mutation S:K147E one can use S:147E or S:K147E to find sequences with this mutation. It would be nice to be able to use S:K147 or S:147K (or even S:147) to look for the un-mutated form.