Use native map when possible

Implemented on all modern browser.

There is a small behavior difference between $.map and Array.prototype.map
but we don't rely on it.

(jQuery flatten arrays and filters null-like)
Fix bug where cell toolbars are not redrawn,
when cell metadata is changed.
Add REST API for retrieving, storing and updating config
Fix docstring, validate JSON on PUT
Apply JSON config updates recursively
Fix writing JSON on Python 2
Return updated config from PATCH requests
allow js tests to run with tornado 4 and phantomjs
forward-port draft76 websockets

from tornado-3.2.2

only enabled during testing with phantomjs
don't pin tornado<4 on travis
bump minimum tornado version to 4.0

remove various websocket workaround for tornado 3
DEV: Forward this_class in container traits.

Makes it possible to do things like List(This()) and have This()
correctly refer to the parent class.
DEV: Add ForwardDeclaredType and ForwardDeclaredInstance trait types.

These traits take advantage of the this_class attribute to resolve a
supplied name relative to the module in which the containing class was
defined.  You can hack this already by leveraging `__name__`, but this
implementation makes it a bit clearer what you're actually trying to do.
STY: Whitespace between class definitions.
BUG: Use hasattr '_resolve_classes' instead of isinstance(Instance).

Fixes a bug where Sequences of Type didn't have their klass correctly resolved.
Move forward-declaration tests to their own section of test_traitlets.
DEV: Support default_value in `ForwardDeclaredMixin`.
DEV: Convert a stray import_item -> self._resolve_string.
DOC: Clarify docstring for `ClassBasedTraitType`.
Add type parameter for contents GET requests