Manage the use of custom html

[ekraffmiller]

Currently the Dataverse UI has several places where the user is allowed to input custom html - for example in Dataverse and Dataset descriptions and other metadata fields, as well as with some previewers.

We want to avoid injecting html directly into the SPA, so for the MVP SPA implementation we will convert the custom html into markup.
However we need to investigate further all the usages of custom html in the Harvard Dataverse and other installations, to come up with a comprehensive plan for dealing with it.

This issue is for summarizing the current usage of custom html, and deciding how or if we want to support it in the new frontend post-MVP