Show weather forecast in DeskClock.

Currently querying the GenieWidget; if it's not present, no
weather is shown or even hinted at in the UI. If GenieWidget
is available but fails to respond to the query, we show
"Weather unavailable." (needs i18n)

Note that Genie's WeatherProvider is currently broken, so
for now you'll always see "Weather unavailable."

Other changes:

- Fix dimming/flashing on rotation.
- Fix other layout problems & inefficiencies.