Added CSS for improved MarkedAsWatched display

Added CSS rules for new iswatched display, what this does;
* Adds a grey background
* Adds a [thicher] strikethrough
* Adds a blueish TICK at the right-hand side

Apart from the major additions;
* Changed the margin on .progress to removed 3px from left side as there is already 3px padding on the left side
* Changed .event > a > span to remove the > span as it didn't seem as though it was needed and (i think) it affected new watched display.