Issue #39: Animate Button Clicks to Provide User Feedback

V1 -> V2:
    1) Remove styles for disabled button.
    2) Add styles for .btn-normal.

Users expect visual effect when they rollover or click a button. In
this patch, we added CSS rules for 2 button states: rollover(:hover)
and click(:active).

    Tested on Firefox 22, Chrome, Safari, Opera, IE9, and IE10.

Signed-off-by: Hongliang Wang <hlwang@linux.vnet.ibm.com>