shell: Relayout the containers page

Fixes #1395
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
base: Provide cockpit.transport.origin property

This is the same as window.location.origin, but we cannot rely
on the latter, since it is not supported by Internet Explorer,
even version 10.

Add documentation and tests.
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
base: Implement transport.filter() and transport.inject()

These methods allow one to filter incoming messages and inject
outgoing messages. Needed when forwarding WebSocket via another
web frame.

Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
ws: Cleaner channel-seed suffix

channel-seed should generally be used as a prefix. So add a
separator in to the mix from the very start.

Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
base: Expose the transport options from the "init" message

This is similar to exposing channel.options. Necessary for forwarding
WebSocket to another iframe.

Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
base: Channels to the right host provided by the init message

The default-host is now carried by the init message. We use this
to determine the default "host" field in channels.

Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
base: Send cockpit protocol via parent frame where possible

Instead of each frame opening up their own websocket, send
messages via the parent frame if possible.

Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
shell: Don't add our own properties to a frame window.

They get removed when the frame content loads.
shell: Register child windows directly.

Instead of finding them again by name.  This is more direct and it
becomes a internal detail of register_child that it associates peer
information with windows via the name.  (Ideally we would use the
Window object itself as the key in a hashtable...)
shell: Use explicit fallback when transport options are not set yet.

This will cease to happen once the shell looks up the packages before
loading external pages.
base: Don't delay opening of a ParentWebSocket.

Instead, do it immediately when returning to the event loop.
base, shell: Be more careful when forwarding control messages.

The "init" command is never forwarded, and non-broadcast messages in
the control channel are only forwarded to their corresponding peer.

Closes #1400.
bridge: Add default arg to cockpit_channel_get_bool_option()

So that we can tell the difference between unset and FALSE.
bridge: Rename the old dbus code out of the way

So we can implement new stuff with the usual 'cockpit.dbus' and
CockpitDBusJson names.
doc: Document and design new dbus-json3 protocol payload

There will be additions later, but this is the meat of the
protocol.
bridge: Implement a new dbus-json3 protocol payload

This protocol is much simpler than the others. There will be some
additions to it in the future, but at it's core it's about relaying
messages and signals.

We don't have innate object manager support in the bridge, the
javascript code will respond to events and update an object model
there.
base: Implement a javascript client for new dbus-json3

This implements a simple javascript client for dbus-json3. It has
no proxy support at this time, but that will be added later.

Fixes #1352
Fixes #1355
doc: Add documentation for cockpit.dbus and related

Closes #1356
bridge: Add explicit 'type' support for dbus-json3

You can specify the 'type' of a call, and then no Introspect() will
be needed when calling the method. In addition, the 'type' will be
returned in the reply.
bridge: Add support for flags in dbus messages

The only thing we do now is report the endianness of the message
as a flag. But in the future this is where things like the new
PERMIT_INTERACTIVE_AUTHORIZATION flag will go.

Fixes #1358