[Data/Feature] a little urlData added + ability to specify high z-index to CU overlay in the urlData

(We don't want to make CU overlay z-index high overlay on every site, since then it would show above elements like the "share" dialog on facebook)
[CSS] give a very light and transparent green tinge to the selected CU overlay
[Data] Improved linkedIn urlData
[CSS] make overlay markers rectangular + slightly change selected CU overlay background color
[Fix] Fixes #179

- fix  the "space issue on youtube" on *flash videos* by using elementAllowsSingleKeyShortcut() which includes a check for embedded elements, and fix the issue on  *HTML5 videos* by checking for the <video> element and the classes for video elements ancestors used on youtube
- if these classes are non-standard, we might need a fix for other popular video sites as well (if/when use HTML5 for videos)
[Feature/CSS/Data] Add code to put a brief "spotlight" on the CU on selection if this is specified in the urlData for the webpage -- useful for webpages where the CUs are hard to spot like pinterest

Also, changed the regular highlight for the selected CU (the subtle one which is meant to stay) to a light gray instead of light green, to use it a neutral color tone