Send name & uuid to capable clients

Add spice_server_set_name() and spice_server_set_uuid() that allows
the client to identify a Spice server (useful to associate settings
with a particular server)

The SPICE_MSG_MAIN_NAME and SPICE_MSG_MAIN_UUID messages are only sent
to capable clients, announcing SPICE_MAIN_CAP_NAME_AND_UUID.

messages.h

@@ -149,6 +149,15 @@ typedef struct SpiceMsgChannels {
     SpiceChannelId channels[0];
 } SpiceMsgChannels;
 
+typedef struct SpiceMsgMainName {
+    uint32_t name_len;
+    uint8_t name[0];
+} SpiceMsgMainName;
+
+typedef struct SpiceMsgMainUuid {
+    uint8_t uuid[16];
+} SpiceMsgMainUuid;
+
 typedef struct SpiceMsgMainMouseMode {
     uint32_t supported_modes;
     uint32_t current_mode;