Allow user to set default CouchDB parameters

[hmaier-fws]

Issue Description:

Users should have the ability to configure default parameters for connecting to a CouchDB database. Since the settings are stored as plain text and can be exported as part of the mdEditor recordset, passwords should not be saved as a default setting.

Required features:

• Settings should be stored following model proposed by Refactor publish-options in user settings to support multiple endpoints #726
• Add a "CouchDB" panel under the Settings menu, "Publishing Settings"
• "CouchDB" panel should allow the user to specify one or more of the following: CouchDB URL, CouchDB Name, Username
• The "Sync" screen should supply values for the appropriate fields if they are defined as default settings, with the CouchDB URL value being obtained from the settings "publishEndpoint".

Proposed CouchDB settings schema

"publish-options": [
  {
    "publisher": "couchDB",
    "publishEndpoint": "url to CouchDB server (string)",
    "couchDbName": "database name (string)",
    "couchDbUser": "database user name (string)"
  }
]