Cloudeebus via Crosswalk extension

The basic idea is this:
- run the Python side inside the Crosswalk extension process
- load the JavaScript side into Crosswalk from the extension
- replace the WebSocket communication with Crosswalk internal
  message passing

Because each app gets its own instance of Cloudeebus and thus its own
private connection to D-Bus, this solution does not suffer from the
security issues of the WebSocket-based Cloudeebus (circumventing D-Bus
access controls, services not seeing the real app).

On Tizen, the services see a normal app process talking to them via
D-Bus.

The Python side gets split it into the main executable using WebSocket
and the core engine which only uses objects providing certain
WebSocket APIs. The Crosswalk extension uses the engine with dummy
objects that map the WebSocket APIs to Crosswalk extension message
passing.

cloudeebus.js, xwalkcloudeebus.py and engine.py must be installed in
the same directory. xwalkcloudeebus.py (or a symlink to it) and a
symlink to libpycrosswalk.so must be in a directory that Crosswalk
searches for extensions.
examples: usable with Crosswalk extension and web socket

When the browser already provides the "cloudeebus" module, then the
examples do not need (and shouldn't) import the cloudeebus .js again,
because that would replace the browser extension implementation with
the web socket version.