myDash: Extend appIcon with click action settings.

Updated after  gnome-shell 3.14: he activation function has been renamed and
its signature and behaviour slightly changed. Update accordingly.
MyDash: restore dash actor internal top alignment after 3.6 release.

The centering of the dash is managed by a further container actor in my
extension. Since Gnome-Shell 3.6 the upstream dash is also centered but the two
centered boxes were causing the misplacement of the dash actor.
myDash: remove accessibility shortcuts duplicate after 3.8 release.

Gnome-Shell 3.8 compatibility.

Since Gnome-Shell 3.8 the accessibility shortcut of the dash is registered
inside the dash code. However I've been extending it adding show/hide callbacks
inside the dockedDash class. Thus I remove it.
MyDash: Use new 3.8 menu-state-signal instead of my old custom code.

Note: isMenuUp variable was removed from appIcon. Some code need to be changed
still.
myDash: Since 3.8 DashItemContainer is a proper St.Widget.

Following upstream code this means that the "Chinese boxes"
(ShellGenericContainer actor inside the DashItemContainer class) has gone and
the code is simplified.
myDash: add option to display applications button at top of dash.
myDash: drag correctly when height is expanded.

Correctly drag icons when the height of the dash is expanded. Compute the total
height of the icons by summing their heights instead of using the container
height.

Conflicts:
	myDash.js
MyDash: bug: few global signals to disconnect.

Few global signals remained connected after disabling the extension, causing
'invalid workid' errors. This had became worse after with the new lockscreen
(GS 3.8 ?) extensions have started to be disabled on lock.
MyDash: bug: with  ignore nautilus desktop window when cycling through windows.

In Gnome Shell 3.10+, not sure about previous versions , the nautilus desktop
window is included in the list of app windows and in the windows count. This
was preventing the functioning of the cycle throug windows option and was
assigning the wrong number of running windows to the app indicator.