Improve change of identity of a proxy config.

- Add the function linphone_address_equal().
- The comparison of two proxy config addresses now returns one of these three values: equal, weak-equal or different.
- If the new proxy config identity is equal to the previous one, a call to linphone_proxy_config_done() does not
unregister and does not delete the sal op. If it's weak-equal the sal op is destroyed but the unregister is not
done. Finally, if it's different the unregister is performed and the sal op is destroyed.
Update oRTP and mediastreamer2 submodules.
Add LCSipTransports wrapper in the Python module.
Fix account creation in Python.
Fix linphone_proxy_config_is_server_config_changed() to return weak-equal if the identities are weak-equal but the proxies are equal.
Fix the use of SipTransports in the Python module.
Add port getter/setter
Prevent downloading rootca at each build when building with CMake.
Update call tester for Python module.
Fix threading issues in the Python module.

Reinitialize log serialization only when all the linphone cores have been destroyed.