Propagate errors from the YouTube player

* sets the 'error' property and notifies event listeners when the
YouTube player indicates an error
Fix: do not modify default options when instantiating shim

* the method used to extend the default options with user-specified
options modified the default object in memory, causing values to become
sticky. If I instantiated a player with option=true and then
instantiated another player without specifying 'option', its default
value would be changed to 'true'.