Picklist/OrderList: expose index of element in ng-template

[benticlaskaris]

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Current behaviour
It's not possible to get the index of the current element in ng-template

Expected behaviour
Exposed index to do additional styling to elements (i.e. style first 5 elements differently)

Minimal reproduction of the problem with instructions
Simply use a p-picklist in your template. S
What is the motivation/use case for changing the behaviour?
Our picklist should display different styling based on position. It can be accomplished doing additional logic (i.e. checking for element position in array) but can really slow the component because it's executed a lot of times

Please tell us about your environment:
OSX, WebStorm, NPM

Angular version: 4.3.2

PrimeNG version: 4.1.2

Browser: all

Language: all