TEIIDDES-1916: Moves the initialisation of password provider implementation

* TeiidDataSourceFactory
 * The only class that requires the password provider, it should be
   responsible for getting it.
 * Getting the provider only when it is directly required, allows for the
   implementing plugin to have been activated and available. Even it is not
   then the data source will not be created and the user should add the
   password to the profile. An altogether less catastrophic outcome!

* DqpPlugin
* TeiidServerManager
* PreviewManager
 * Removes all responsibility for the password provider from these classes
Avoids exception generated in logs when installed

* The action sets initialiser is unable to find the jdbc_import icon,
  presumably due to the plugin not having been activated when designer is
  newly started.
* Adds a copy of the icon to the designer.ui plugin to avoid a needless
  dependency.