- better integration with network reachability callback
- fix crashes (mTunnelClient can no longer be NULL)
- avoid useless operations during transcient states
- clarify source code
- allow the application to set root_ca before the tunnel connection actually starts.

fix the tunnel tests, that were not working correctly.

Some booleans have been replaced by a state variable

* The tunnel manager are now thre mode : disable, enable and auto
* Two new functions: linphone_tunnel_set_mode() and linphone_tunnel_get_mode()
* linphone_tunnel_enable(), linphone_tunnel_enabled(), linphone_tunnel_auto_detect()
and linphone_tunnel_auto_detect_enabled() are now deprecated.

* TunnelManager does not implement the TunnelClientController anymore
* Methods which are not uses by functions of linphone_tunnel.h have been turn to private
* Private methods which are not used by any other methods have been deleted
* Unused attributes have been deleted

If this parameter is set to 1, SIP packets will pass through tunnels when the
tunnel mode is enabled. If set to 0, SIP packets will be directly sent to proxies
whatever the state of tunnels

- move TUNNEL_ENABLED to config.h, which avoids recompilation issues with -D flags.

- move TUNNEL_ENABLED to config.h, which avoids recompilation issues with -D flags.

- API cleanups
- add http proxy support
- add stubs to avoid using conditional defines.