onFocus support for autocomplete

[ydubey]

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Plunkr Case (Bug Reports)
Please fork the plunkr below and create a case demonstrating your bug report. Issues without a plunkr have much less possibility to be reviewed.

http://plnkr.co/edit/D1AK7i

Current behavior
Cannot add onFocus listener to autocomplete.

Expected behavior

Minimal reproduction of the problem with instructions

What is the motivation / use case for changing the behavior?
I want to be able to conditionally show suggestions show() when autocomplete is focussed.

Please tell us about your environment:

• Angular version: 2.0.X

• PrimeNG version: 2.0.X

• 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 ]

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

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