[SysApps] Add the convenience classes and prototypes

These C++ classes and JavaScript prototypes are helpers for the common
places that appear all around the SysApps APIs specifications.

The main features are:

- Helpers for creating objects managed by the extension.
- Easy way of declaring API methods.
- EventTarget implementation, and thus, helpers for dealing with
  events.

For more information, check the documentation on the code.
[Sysapps] Add unit tests for the convinience classes
[Sysapps] Add browser tests for the common JavaScript API

These tests are testing the functionality of the helper JavaScript
prototypes and objects, like the EventTarget.
[SysApps] Add Raw Sockets stub

Just the skeleton to serve as base for the interfaces implementation. No API is
currently exposed.
delta
[SysApps] Add the RawSocketObject

This class is going to concentrate all the shared code among
the different interfaces of the Raw Socket API. Currently only
the ReadyState is shared.
[SysApps] Make it possible to create a TCPSocket from a connected socket

The TCPServerSocket will need to create a TCPSocket from incoming connections.
This patch makes it possible to create an object in the native side first and
handle the identifier to the JavaScript context.
delta
[Sysapps] Add browser tests for the Raw Socket JavaScript API

Tests if the objects are leaky and if the basic functionality like
send and receive data works. These tests are not API conformance tests.