Global menu support

Registered by Fabounet

Add support for the global menu.
First support the Ubuntu's implementation, that works on Dbus.
Make the code so that other implementations can be supported in the future.
The applet's icon should give the ability to:
- close, minimize, restaure, close the current window
- display the menu of the current window in a 1-menu style (not a menubar)

Blueprint information

Status:
Started
Approver:
Fabounet
Priority:
High
Drafter:
Fabounet
Direction:
Approved
Assignee:
Fabounet
Definition:
Approved
Series goal:
None
Implementation:
Beta Available
Milestone target:
None
Started by
Fabounet

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