Refactored the watch/unwatch icon for Vector.

Refactored the watch/unwatch icon for Vector.
1. Changed from using an image to a div with background images.
2. Redesigned the star icon, and implemented it as a sprite with unique watched/unwatch and normal/hover versions.
3. Designed custom spinning star icon - used while waiting for server to respond.
4. Added $wgVectorUseIconWatch setting to default preferences (defaults to false) and added support for enabling and disabling the feature.
5. Got rid of old now unused icons.
6. Changed styles and ajaxwatch.js code so that javascript is not needed for hovering
7. Changed ajaxwatch.js code to work with the div icon rather than the previous img setup.
8. Regenerated RTL versions.