Implement RFC85 Dynamic Virtual Study

[forus]

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

Describe changes proposed in this pull request:

• Added option to select a dynamic type of virtual study while creating it
• Static type (the legacy one) is the default one

Checks

• 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.
• The commit log is comprehensible. It follows 7 rules of great commit messages. For most PRs a single commit should suffice, in some cases multiple topical commits can be useful. During review it is ok to see tiny commits (e.g. Fix reviewer comments), but right before the code gets merged to master or rc branch, any such commits should be squashed since they are useless to the other developers. Definitely avoid merge commits, use rebase instead.
• 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!

Any screenshots or GIFs?

If this is a new visual feature please add a before/after screenshot or gif
here with e.g. Giphy CAPTURE or Peek

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[pieterlukasse]

Thanks @forus !
I added some proposals to improve the tooltip text.