Integrate cdot API in variant query

[holtgrewe]

Is your feature request related to a problem? Please describe.
In #100, we implement a more advanced backend API for mapping between coordinate systems. This is not exposed to the user.

Describe the solution you'd like
Try to map the user's input using cdot. If this yields a GRCh37/GRCh38 genomic variant then use this rather than going (100% unsuccessful anyway) to the simple genomic representation or gene IDs.

Describe alternatives you've considered
N/A

Additional context

• Add cdot-based backend for mapping between coordinate systems #100