libnetconf UPDATE YANG data configuration

Configuration based on YANG data. Open 2 ssh channels on one
session. Pubkey,interactive,pw,none SSH authentication working. SSH
message callback not a callback anymore, handle SSH messages manually.
ietf-netconf-server and all models it imports added and a libnetconf2 own model
with augments. And finally only local-definition of keys supported. 2 tests.
NBC API changes.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2a29e96..4740567 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -111,7 +111,8 @@
     src/messages_server.c
     src/session.c
     src/session_client.c
-    src/session_server.c)
+    src/session_server.c
+    src/config_server.c)
 
 if(ENABLE_SSH)
     list(APPEND libsrc
@@ -136,7 +137,8 @@
     src/session_client.h
     src/session_client_ch.h
     src/session_server.h
-    src/session_server_ch.h)
+    src/session_server_ch.h
+    src/config_server.h)
 
 # files to generate doxygen from
 set(doxy_files