Add a C wrapper around the dbus API

<lool> tvoss and my official positions on APIs backed by DBus services is that
       a C library wrapping them is preferable [12:32]
<lool> with corresponding QML bindings
<barry> so they don't make direct dbus calls, but instead call into the c api?
<lool> that is, for regular QML/Click apps or C/Click apps, we'd want them to
       use QML bindings or C API to interface with our middleware
<lool> right

Upon further discussion, we can except the upgrader for the short term because it's all in the OS. Thus the priority on this is lower than integrating the UI unless this blocks that work.