TinkerforgeBinding enhancements

Related to issue 207 https://code.google.com/p/openhab/issues/detail?id=207:

New devices:
    * Bricklet Industrial Quad Relay
    * Bricklet Industrial Digital In 4
    * Bricklet IO-16
Incompatible Changes:
  * LCDBacklight is a sub device of LCD20x4 Bricklet (items file must be changed)
  * LCD20x4Button posts an update not a command anymore (rules must be changed)
  * IndustrialQuadRelay sub id numbering now starts from zero (items file must be changed)
Bugfixes:
  * Missing updates of Items if a Tinkerforge Device is referenced in several Items
Other changes:
    * support for serveral Item types
       * NumberItem
       * SwitchItem
       * ContactItem
   * updated Tinkerforge API to 2.0.12
Structural changes:
   * support for digital sensors and actuators in the model
   * all updates to the event bus use one method: TinkerforeBinding.postUpdate()
   * on bindingChanged events all item values are updated
   * when a device is enabled it fetches the current state from TF device and updates the model value, in fact updates are send to the event bus
   * handle disconnected brickds
      * on startup make retries every second
      * when running use the Tinkerforge auto reconnect feature
   * added a Readme.md to the bundle to document the changes