adding datasets version 16.15.0

There's a new version of datasets!

According to the release page it looks like most of the changes are to documentation, but there are also some bug fixes.

In truth, there's a version more current that this one, but it's missing its pre-compiled binary. I find that very suspicious.

All I did was update the version arg:

$ diff ncbi-datasets/16.10.3/Dockerfile ncbi-datasets/16.15.0/Dockerfile
3c3
< ARG DATASETS_VER="16.10.3"
---
> ARG DATASETS_VER="16.15.0"

Pull Request (PR) checklist:

[X] Include a description of what is in this pull request in this message.
[X] The dockerfile successfully builds to a test target for the user creating the PR. (i.e. docker build --tag samtools:1.15test --target test docker-builds/samtools/1.15 )
[X] Directory structure as name of the tool in lower case with special characters removed with a subdirectory of the version number (i.e. spades/3.12.0/Dockerfile)
- [X] (optional) All test files are located in same directory as the Dockerfile (i.e. shigatyper/2.0.1/test.sh)
[X] Create a simple container-specific README.md in the same directory as the Dockerfile (i.e. spades/3.12.0/README.md)
- [X] If this README is longer than 30 lines, there is an explanation as to why more detail was needed
[X] Dockerfile includes the recommended LABELS
[X] Main README.md has been updated to include the tool and/or version of the dockerfile(s) in this PR
[X] Program_Licenses.md contains the tool(s) used in this PR and has been updated for any missing

StaPH-B / docker-builds