Applied ui-tweaks patchset.

Applied ui-tweaks patchset.

- prettyprinter now does syntax highlighting of Factor code
- added a prettyprinter.stylesheet vocab
- text shadow character style for formatted streams
- text shadow for labels
- toolbar buttons display keyboard shortcut in status bar rather than in the button title
- changed some colors in help.stylesheet to match the colors in Factor's scrollbars and border-buttons
- changed status bar color to match the dark blue in Factor's scrollbars
- added some internal padding to the browser gadget to give the article content some breathing room

NOTE: I removed the "pane" slot from browser-gadget. The slot was never used (at least in my image), and now that the browser-gadget's help-pane is wrapped by a "border" gadget, the slot name would be misleading.