Bug 919913: Add send methods to RawDBusConnection, r=qdot

This patch adds methods for sending DBus messages to the class
RawDBusConnection. There are 3 types of interfaces.

 - Send             Sends a message over DBus. No error checking or
                    handling of replies is performed. These methods
                    do not block the sending thread.

 - SendWithReply    Sends a message over DBus and runs a call-back
                    function for the reply. This should be the default
                    case for most scenarios. These methods do not
                    block the sending thread.

 - SendWithError    Sends a message over DBus and waits for the reply
                    or an error. This interface has only been added for
                    some existing code that can safely block the sending
                    thread. Don't use it in new code.

These 3 types of interfaces represent what is currently used of the
existing send functions in DBusUtils. When all users have been converted
to the new methods, the interfaces in DBusUtils can be removed.
Bug 919913: Converted BluetoothDBusService to new Send methods, r=echou

This patch changes BluetoothDBusService to use the new send methods
that have been added to RawDBusConnection. The conversion from the
old functions is

 - dbus_func_send to Send,
 - dbus_func_send_async to SendWithReply,
 - dbus_func_args_async to SendWithReply,
 - dbus_func_args to SendWithError, and
 - dbus_func_args_timeout to SendWithError.

References to DBusCallback have been removed.
Bug 919913: Cleanup DBusUtils, r=qdot

This patch cleans up the DBus utilitys and helper classes. All functions
for sending have been removed. Their users have been converted to the
new methods in RawDBusConnection. Include statements have been cleaned
up as well. Some methods of DBusMessageRefPtr have been moved from the
header to the source file to prevent inclusion of the DBus API from within
the header file.
Bug 919913: Introduce DBusReplyCallback, r=qdot,echou

DBusReplyCallback replaces the removed DBusCallback as type for
reply-handler functions. Bluetooth, the only user of DBus, has
been updated as well.
Bumping gaia.json for 2 gaia-central revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-central/rev/e7b0d65fb83f
Author: Greg Weng <snowmantw@gmail.com>
Desc: Merge pull request #12561 from snowmantw/issue919858

Bug 919858 - [LockScreen] Enhance the UI experiments when unlocking the phone with one hande

========

https://hg.mozilla.org/integration/gaia-central/rev/20efa00c07b0
Author: Greg Weng <snowmantw@gmail.com>
Desc: Bug 919858 - [LockScreen] Enhance the UI experiments when unlocking the phone with one hande