Fix up GUI interactions with animation start/stop

 * Clicking Pause button when in MapMode (not AnimationMode) no longer removes the visible overlay
 * Play / Pause Buttons are enabled/disabled to prevent user from starting two overlapping animation sequences
 * Colored the buttons, used standard Bootstrap classes: btn-success and btn-warning for playing/pause, respectively.  Imperfect but OK I think.
 * Pulls the map legend inside the Map when browser width is reduced (it was standing-off-from-left, which made it stick out in some cases).