Refine cast list on play info pages

[cmil]

The cast list on play info pages still looks a bit improvised to me. Here are a few suggestions:

• more clearly separate it from the content to it's left (on desktop screens) either by a background or border
• don't indent the heading (it somehow looks odd to me)
• make scrollbar more subtle
• only show it on the network tab (also see Add widget with scenes/acts in full-text mode #76)
• nice to have: some gradient at the bottom (and top when scrolled) to indicate that there is more content to scroll to
• on the iPhone there is a relatively large gap between the network graph and the cast list which could maybe be reduced a bit