typeahead-focus-first=false option to prevent first match from being focused

Fixes #908.

Should be 100% backwards compatible with existing markup and functionality.

Current functionality (first result is automatically focused as you type):
``` <input typeahead="..."  /> ``` 

New functionality (first result is NOT automatically focused as you type):
``` <input typeahead="..."  typeahead-focus-first="false" />``` 
I copied this from isEditable on line 50 which is also default-true. Line 60 for appendToBody is default-false. If you prefer different style for default-true attributes, I would suggest updating both isEditable and focusFirst, but I think that's outside of the scope of this pull request.