Cherry-picked commits from e95

Created by: muffato

Description

Those commits have already been reviewed and accepted on the release/95 branch, see #312 and #313. This PR is to copy them to master

For all the other sections of this template, see the original PRs for more details. There is

1. a fix to handle undefined values when filtering whole-genome alignments
2. a change to allow the real list of whole-genome alignments methods available in the database, rather than an hard-coded list

Testing

Have you added/modified unit tests to test the changes?

yes

If so, do the tests pass/fail?

yes