Autocompletion for the method parameter settings

[stof]

when configuring the custom method references in the plugin settings, it would be good to provide autocompletion for classes/interfaces in the callTo field (which should probably have a more meaningful label as the callTo is on class+method IMO) and then on the method field (based on the defined class).

Btw, the doc should probably be updated too because it describes writing \Knp\Menu\ItemInterface:addChild:1:route:array_value:route whereas the interface provides 6 separate fields.