The default coll parameter to assets is the database name

[acwhite211]

Fixes #6160

The default coll parameter to assets is the database name. This is determined when calling the /context/attachment_settings.json API endpoint, which call the assets_gw app view function get_settings. When setting the default coll parameter, it should be the database name in the settings, not a random collection name.

Checklist

• Self-review the PR after opening it to make sure the changes look good and
  self-explanatory (or properly documented)

Testing instructions

• Open assets page for an instances with attachments on the attachments server
• See that all the attachments are fetched successfully