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