Introduce OS_TIZEN and set specific settings for Tizen platforms

This includes disabling site themed scrollbars (we use overlay
scrollbars always), enabling double tap to zoom for zoomable pages,
disable auto playing of music (a touch is needed) as well as
moving input fields into the view when focused.

It also enables the fade out scrollbars on all Tizen platforms, not
just mobile.
Merge pull request #76 from kenchris/settings

Introduce OS_TIZEN and set specific settings for Tizen platforms