Imrprove boost-dbus high level interfaces

This commit has been squashed fromt the dbusproperties branch, and adds
quite a few pices of functionality.

1. Template called element_

Imrprove boost-dbus high level interfaces

This commit has been squashed fromt the dbusproperties branch, and adds
quite a few pices of functionality.

1. Template called element_signature that can sucessfully map complex
c++ types (like std::vector<std::string, variant>) to their equivalent
dbus signatures at compile time.
2. Implements a high level dbus interface that exposes properties,
objects, and interfaces as first class c++ objects, and manages their
lifecycle correctly. See unit tests for examples.
3. implements variadic template registration for lambda functions, such
that function prototypes are automatically determined at compile time,
thus removing the requirement to do this by hand for each interface.

Change-Id: I43efed4fc63f7e2d69ac85918e0f6d3011a12d86

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