Support GMenu indicators

It looks like this will be very possible.

The merges need to happen starting with wingpanel version 150:

http://bazaar.launchpad.net/~elementary-pantheon/wingpanel/0.3.x/revision/150

Done?

Maybe I got this done.

This patch is a collection of indicator-related cherry pics from Wingpanel r150 onward.

Can confrim os-patch-indicator-datetime trusty and os-patch-indicator-sound-trusty working.

Good news: indicator-datetime, indicator-session, and indicator-sound all work!

Bad news: indicator-session and indicator-sound are out of place, immediately to the right of indicator-datetime (which is correctly on the far left). I suspect they are all on the left end because of some unimplemented sorting for the unity indicators.

So far tested inly in slim mode.

indicator-datetime (os-patch-indicator-datetime-pantheon) is unstable with super-wingpanel.

It usually appears for a while at the beginning of the session and then blinks out of existence sometime later.

Also, the calendar never appears.

I can't be sure if this is because of the newer version of indicator-datetime missing something it wants to interact with or if it just doesn't like super-wingpanel.

Compatibility for Unity 7 system indicators

indicator-datetime seems to have stabilized with the new sorting. I actually expected that would happen!

Apparently indicator-datetime is very particular about it's placement, and won't tolerate being to the left of indicator-appmenu.

So, as shown in the patch above the appmenu must appear first in the list of indicators and datetime after it.

Still a little bugginess though: datetime sometimes loses the "Time and Date Settings" link and occasionally the clock (the indicator is still there, and can be clicked on, but appears as an empty gap between appmenu and keyboard)