taxon-descriptions merging

[adam-collins]

The merging function of taxon-descriptions is incomplete.

1. Cleanse the html content

• Start by scanning tags and attributes, logging them, followed by filtering to include only the "approved" list.
• Document this "approved" list.

2. Document a process that make is simple to do adhoc item updates. Note that taxonIds can change and this should be covered.

[adam-collins]

Added aggressive santization to the html content.
Outstanding is documenting the adhoc item update process.

[adam-collins]

Made changes so the admin UI can override individual descriptions. Overrides live in postgresql.

Now need to fetch these overrides and apply them when rebuilding merged data.