smaller hello packet

[totaam]

There are too many things in it and most of them aren't really needed for the handshake.
There may be multiple hello packets sent when we're dealing with authentication and this is just a waste of space and bandwidth, it makes it harder to see what is really going on too.

• 3e42b61 was needed to process the handshake for clients that don't provide the full "keymap" data and 7d344bc sends the keymap data after the handshake.
• a71583d removes some detailed OpenGL attributes - can be re-enabled with XPRA_FULL_INFO=2 (so somewhat related to Allow to disable sending unneeded user data to the server #3582)
• c873c71 skips exposing the theme's icon names

TODO:

• too much platform details
• sound properties are mostly unused
• icc data should be synchronized and sent separately

See also #3582

[totaam]

With the changes above and logging with XPRA_LOG_RAW_PACKET_SIZE=1:

• git master: sending hello : 8529 bytes
• 4.4.x: sending hello : 157968 bytes

Quite the improvement!

There is a minor downside to this: when connecting to older servers, the newer clients won't be sending the icc data at all.. (since by the time we figure out that the server can't handle the new configure-display packet, it's too late and we have sent the hello without it)
And there's still some minor duplication: 2331672