native win32 systray using ctypes

[Antoine Martin]

Split from #678.
As of r15048, the native systray implementation is disabled, we use the statusicon based on, which works well enough in most cases.

[Antoine Martin]

work in progress converting to ctypes, adding guid support, direct pixel to bitmap function, etc

[Antoine Martin]

mostly working patch - mask needs fixing

[Antoine Martin]

Done in r15172, related improvements in r15173 + r15174: the native tray code can be disabled by using:

XPRA_USE_NATIVE_TRAY=0 xpra ...

(applies to both Linux and win32)

Mostly a FYI: launch vlc and its system tray should appear as before.
We supply a unique GUID, so users can configure "tray and notifications" to be enabled / disabled, and those settings will now stick, no matter what version of xpra is installed (64-bit vs 32-bit, launched from gui or not, etc).

[J. Max Mena]

This is long overdue for closure - I haven't seen any issues with tray icons (Steam/VLC/Chrome sometimes) in the last few months despite reasonable amounts of usage. Closing.