Further parameters for connection URLs

In a comment to issue #598, @sparkacus suggested two additional parameters for creating/updating favorites:

- `save_in_keychain` (whether to save the password in the keychain or not)
- `color`

Start by tracing how connection URLs create or update favorites, then review issue #598 for the original context. Confirm how URL parameters are parsed and define the expected handling for save_in_keychain and color. Done means both parameters work for creating and updating favorites without changing existing behavior.

Written by the indexing model from the issue text.