Put server name in tray-menu header

[Philip D Loewen]

Motivation: I often have multiple XPRA connections active at once, and I'd like to be confident about which one I am about to send a command to.

Detail: For each of my XPRA client connections there is an icon in the system tray. (The clients are running on Ubuntu 16.04 with LXDE desktop.) Each icon has a tooltip that shows the server name when the mouse hovers over the icon. It would be nice to see the same string exactly provided as a static title line on the menu that is presented when I select the icon by clicking it. Rapidly clicking the icons in sequence feels faster than waiting for each tooltip, and seeing the server name right in the menu when it opens would add a little reassurance before the next click sends off a signal.

[Antoine Martin]

Was easy enough, so done in r19614.

Note: this doesn't apply to macos, which does everything different.

Please try the latest beta builds from there: https://xpra.org/beta/ and close if that works for you.