Normalize text with HTML or XML tags into standardized HTML output

[helrond]

Is your feature request related to a problem? Please describe.

Text coming from ArchivesSpace may contain XML or HTML tags. These tags are processed, indexed and ultimately rendered as strings in DIMES.

Describe the solution you'd like

Pass text fields through a pair of transformers which normalize HTML and XML to a uniform HTML output. The XML transformer should offer an XLST, while the HTML transformer should provide rules for filtering HTML. Both of these transformations should be configurable (meaning defaults for the XLST and HTML filtering rules should be provided but overideable through application configuration).

Describe alternatives you've considered

See #507 for a short-term solution.

Additional context

In order to provide consistency in the API, we may need to convert text which does not contain HTML or XML tags into the same expected HTML output.