Engine: Added first implementation of Actions and Actors.

Glib now requires a separation between menus and their actions. Actions
can be accessible globally or locally and reused in menus, toobars, ...
and basically everywhere depending on their context, ie their UI window.

The current engine principle was relying on actions between exposed in
real time when the appropriate object representation in the UI was
selected.

We are now introducing a new concepts where objects (derived objects or
parent classes or ServiceCores) can expose Actions through Actors.

We have two implementation of Actions:
- The base class, simple
- A derived objects dedicated to ContactActions
Call History: Turn the book into an Actor.
Engine: Added GTK+ (GIO) representation for Actors and their Actions.
UI: Added preliminary support for Actions in the main window.

Mainly in the call history view.

Also converted the actions toolbar into a header bar.

This is still a POC.
Fixed compilation.
ActorMenu: Fixed menu creation and actions handling.

add_gio_actions methods were added to both ActorMenus objects.

They allow adding Actions at the global GIO level.

ActorMenus and ContactActorMenus add GIO actions at the application
level. Window specific actions are typical of the user interface, while
it is logical to have engine actions accessible globally.

ContactActorMenus should only expose actions when the (Contact,uri) tuple
given as data is valid for the given action. Having two different
add_gio_actions implementations that are called from the constructor
required the creation of a static C++ class method in order to create the
object, then initialize it with the proper add_gio_actions method.
Call History: Generate the proper popup menu on contact selection.

This uses the new ActorMenu/ContactActorMenu widget.
Main Window: Regenerate the window menu on contact selection.

It uses the new dynamic ActorMenu and ContactActorMenu stuff to expose
GIO Actions defined through the Action/Actor engine mechanism.

It is currently limited to call history contacts.