Make Sandcastle demos prettier

I didn't like the jarring unstyled look of Sandcastle demo buttons and drop downs.
This is my attempt to make them look more like the rest of Cesium.
CSS tweaks.
Merge remote-tracking branch 'origin/master' into sandcastle-buttons

Conflicts:
	Apps/Sandcastle/templates/bucket.css
CSS tweak
resnap pictures
Merge pull request #1985 from AnalyticalGraphicsInc/sandcastle-buttons

Make Sandcastle demos prettier