Expose active window positon on move to reducer

[ppot]

Expose window position {x, y} once the active window when it's moved.

In order to add modularity for plugins:

• The onWindow only expose the window creation. But once the window is created, moved action are not accessible.
• Allow plugins to know the current position of the active window based on the UI_WINDOW_MOVE from the window move action lunched by the RPC.
• Enable better state recording for plugins such as session restoration

[juancampa]

@chabou does this LGTM now?

[chabou]

Thank you for your help @ppot