MessageService clear()

[Suncrusher]

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Current behavior
It is not possible to remove currently displayed messages via the message srevice.

Expected behavior
When calling messageService.clear(), previous added messages are removed.

What is the motivation / use case for changing the behavior?
When using the message service to add messages then there should be a possibility to remove the messages via message service - using the same way.

Please tell us about your environment:
Win 7, 10, npm

• Angular version: 2.0.X
  Angular 4.x

• PrimeNG version: 2.0.X
  PrimeNG 4.2.0-RC.1

• Browser: [all | Chrome XX | Firefox XX | IE XX | Safari XX | Mobile Chrome XX | Android X.X Web Browser | iOS XX Safari | iOS XX UIWebView | iOS XX WKWebView ]
  Chrome, Firefox, IE, Edge

• Language: [all | TypeScript X.X | ES6/7 | ES5]
  Typescript 2.4.2

• Node (for AoT issues): node --version =
  6.10.3