Dropdown should open using the space key

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I'm submitting a ... (check one with "x")

[ ] bug report => Search github for a similar issue or PR before submitting
[X] feature request => Please check if request is not on the roadmap already https://github.com/primefaces/primeng/wiki/Roadmap
[ ] support request => Please do not submit support request here, instead see http://forum.primefaces.org/viewforum.php?f=35

Expected behavior
Pressing the space key should open the dropdown list when the dropdown has focus and the dropdown list is not open.

What is the motivation / use case for changing the behavior?
Mirrors behavior for the native HTML select element (and other similar controls, e.g. angular material's select).

Please tell us about your environment:
Windows 10

• PrimeNG version: 1.1.4

• Browser: All

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Thanks!