Upgraded from NetBeans to WebStorm.

Removed data- prefixes from attributes.
  This was a workaround to remove NetBeans error messages.
  WebStorm can handle custom attributes.
Simplified table style for scoreboard.
Updated angularjs to 1.0.8
Renamed gameover to game_over.
Whitespace: WebStorm 'Reformat Code'
Removed Cell.chains[].

Cell.chains[] was bad.
  A chain contains cells. A cell does not contain chains.
  Contained items better not know about their containers.
Definitions of following functions changed accordingly:
  Chains.bind(cell1, cell2, direction)
  Chain.bind(cell)
  Chain.add(cell)
Sourced underscore.js.

Substituted underscore function calls where appropriate.
Chains.find made private. Chain.bind removed.

Chain.bind is unnecessary. Chain.merge is enough.
Chains.bind updated accordingly.
Styles were simplified.