seqan3 argument parser

[joshuak94]

The first step of introducing seqan3 into vaquita. This pull request does a few things:

1. Add seqan3 as a submodule and switch seqan to a submodule. This allows both of them to be updated automatically in case of errors/bugs.
2. Replace the argument parsers in vaquita with the seqan3::argument_parser
3. Terminate the main vaquita program in case any step returns false.

[joshuak94]

@xenigmax I can't request reviewers...

[joshuak94]

Superseded by #37