Remove EventTarget, and subsequent fallout.

[Hixie]

The primary goal of this change was to remove EventTarget from the
sky_engine C++ code. Since EventTarget is so core to the entire event
system that sky_engine was based on, this is a rather invasive change.
As such, it had some knock-on effects. I deleted some of the files
that were affected, and cauterised the remainder.

In many cases, a file would depend on another file that it didn't
include directly, but instead included indirectly via another file
that I deleted. When this happened, if the features that this broke
were obsolete, I sometimes just removed the features instead.

Specifically:

• removed EventTarget
• removed EventQueue, since without a target, what's a queue going to
  do?
• same with EventDispatch*
• removed ExecutionContext, since it had an EventQueue and nothing
  else it did was relevant to Sky anymore
• removed ActiveDOMObject, which was all about ExecutionContexts
• removed ContextLifecycleNotifier since it dependend on
  ExecutionContext and ActiveDOMObject
• removed the other Lifecycle classes for consistency, and replaced
  them with four booleans in the Document class
• removed some of the attributes that are no longer relevant from
  IDLExtendedAttributes (ConstructorCallWith and
  CallWith=ExecutionContext)
• removed the Document member on DOMDartState since we never set it to
  anything but null.
• removed BuiltinSky::InstallWindow since it relied on the Document
  member of DOMDartState
• removed EventHandler, EventListener, and mentions of those in
  various binding scripts
• removed NewEventHandler, since we're not using that either
• removed the following interfaces from the Sky Dart API:
  • EventTarget
  • EventListener (since without a target, there's no way to listen)
  • FocusEvent (since it's only member was an EventTarget)
  • HashChangeEvent (mostly by accident, but it's defunct anyway)
  • FontFace (it used ConstructorCallWith=ExecutionContext)
• changed the following interfaces of the Sky DART API:
  • MediaQueryList is no longer an EventTarget
  • Node is no longer an EventTarget
  • Document no longer has defaultView (depended on
    DOMDartState's document)
  • DocumentFragment, Element, Range, and Text no longer have a
    constructor (they all depended on DOMDartState's document, which
    is now gone)
  • Event lost its EventTarget members and path.
  • Window lost its WindowTimers partial interface (it used
    EventTarget and ExecutionContext a lot)
• removed numerous hacks in the bindings around features that are now
  gone, like addEventListener
• removed a bunch of console logging code, since that relied on
  ExecutionContext
• cauterised the wound in FontFace.cpp by removing constructors and
  methods that called now-removed features
• same with MediaQuery and friends
• same with some editor features and focus-related features
• same with Document
• removed DOMTimer classes since they use ExecutionContexts

[abarth]

Please remove

[abarth]

LGTM