fixed url handling with reserved characters (fixes #402)

[sio4]

Indeed, #402 is a valid and important issue that users can confuse.

• The cd.URL is a kind of raw value that should be able to directly interpreted by the underlying database engine, so using a plain version (without URL encoding) of the password with reserved characters is not a valid usage. However, when if the user provided a correctly encoded URL, we should be able to parse and store the value in CD structure.
• When we create URLs for database connection, we should be able to generate a correct URL with the parsed CD values, and it should be a valid URL that can be interpreted by the database engine.
• MySQL is an exception since their connection URL is not a standard format.

fixes #402

[sio4]

left comments for future reference