Referenceseeker

This is the first minor release after the JOSS publication.

We updated the pre-compiled RefSeq databases and fixed some minor typos and bugs.

This release archives the to-be-published version 1.6 necessary for the JOSS publication.

In this release we:
- added a `CONTRIBUTING.md`
- added issue templates for bugs and features
- fixed some typos

This release provides an exciting new feature:
ReferenceSeeker now supports the initialization of local, private & custom DBs and the fine grained import of local genomes - either into a fresh new DB or an existing public one.
Therefore, check the new `referenceseeker_db` command - more info in the [readme DB section](https://github.com/oschwengers/referenceseeker#databases)

Additionally, we:
- added a tiny mock DB as a test case -> assure your local installation works as expected!
- improved the documentation (readme)
- applied some code refactoring
- added PyTest-based unit tests
- implemented a GitHub Actions-based CI -> further code quality assurance

This release introduces the **bidirectional** computation of `ANI` / `conserved` DNA values.

Just add the `--bidirectional` option.

Added options:
- `--ani`: set custom ANI threshold (default=0.95)
- `--conserved-dna`: set custom conserved DNA threshold (default=0.69)

This is release is a purely technical update:
- ReferenceSeeker is now on PyPI (https://pypi.org/project/referenceseeker/)
- we dropped any Docker image support
- we dropped the scaffolding feature via MeDuSa in order to speedup a subsequent BioConda migration.