Fix # (see https://help.github.com/en/articles/closing-issues-using-keywords)

Describe changes proposed in this pull request:

• Use clickhouse for density plot calls
• Refactor logic into service to clean up controller
• Simplify logic into Java streams

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• The commit log is comprehensible. It follows 7 rules of great commit messages. We can fix this during merge by using a squash+merge if necessary
• Has tests or has a separate issue that describes the types of test that should be created. If no test is included it should explicitly be mentioned in the PR why there is no test.
• Is this PR adding logic based on one or more clinical attributes? If yes, please make sure validation for this attribute is also present in the data validation / data loading layers (in backend repo) and documented in File-Formats Clinical data section!
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