Plugin configure command

This PR addressed http://teampulse.telerik.com/view#item/275633 and also I need it to implement this story http://teampulse.telerik.com/view#item/275633
There's no need to specify command parameter when you've implemented canExecute method. CommandsService will check for canExecute method first and if it exists, it will use it for validation. So there's no need to use PluginConfigureCommandParameter at all. You can put the code in canExecute.

As currently the command accepts only one parameter and it is mandatory, I think it is better to remove canExecute method. CommandsService will use the allowed parameter and call its validate method. If the validate method returns true, the command will be executed. If the user do not pass a parameter (or passes more than one), CommandsService will fail.