How to re-enable the systray (indicator panel) after latest updates

Try using the Indicator Systemtray Unity (for Ubuntu 14.04 - 15.04):

Indicator, when clicked, shows the tray.

Also there is a display mode "separately from the indicator" - on top of the panel like a dock. In this mode, the position can be changed by scrolling the mouse over the indicator. To change the mode position: press the middle mouse button on the indicator.

Installation in the terminal:

sudo apt-add-repository ppa:fixnix/indicator-systemtray-unity
sudo apt-get update
sudo apt-get install indicator-systemtray-unity

You must then log out and again log in using your user.

https://github.com/GGleb/indicator-systemtray-unity

To remove this package (with its configuration files!!!):

sudo apt-get --purge remove indicator-systemtray-unity