Fix plot legend padding.

Added explicit border-spacing to compensate for global removal of
padding.  Flot should really take care of this itself; layout-critical
styles shouldn't depend on the user-agent defaults.
Expand buttons to match the new page font size.
Expand inputs to match the new page font size.
Generalize placeholder styles.

Give any direct child of demo-containre the same style, so it can be
used for both #placeholder and #overview.
Pad check boxes to match the new page font size.
Add a sub-header style for per-plot labels.
Re-styled and cleaned up all the examples.