Replace InfluenzaDb with ExampleDb from alakazam

[Jason Vander Heiden]

I think we can probably replace InfluenzaDb with the new ExampleDb.gz file from alakazam. The alakazam example has 1000 sequences from day 0 and 1000 from day 7 for 1 subject, with preference towards larger clones. We could maybe add the same for a second subject, if the cross-sample distToNearest doesn't look right across time points.

Any issues with this?

[Jason Vander Heiden]

Replaced with ExampleDb object in c66f66c.