fix: fixed position

This fixes the following typeahead issue. If a typeahead is inside an input with overflow other than visible and position other than static, the popup will be not be shown outside this div.

This makes the popup have position:fixed with appropriate position coordinates. 

See these two plunkers:
current behavior: http://embed.plnkr.co/qbDuGOIZ4YD84e1GoohS/preview
patched: http://embed.plnkr.co/C6M62gz1daolnqRsAtHe/preview