Add example plugin and verify the correct behaviour of the framework

Do not destroy unused SRTP, ZRTP and DTLS SRTP contexts as they may be needed in the future or after a different encryptin scheme is negotiationed due to network latencies

Implement GoClear capability for ZRTP to be able to reenable it later during the call

Split some common code between the XMLRPC and REST API in utils files
Do not create local variable named mRequestCallbacks in AccountCreatorFlexiAPI constructor
Do create objects with new and delete them using free
Complete endpoints integration
Add a new flexiapi_url config variable in the LinphoneCore configuration
Split account creator tests in two, local and xmlrpc ones
Cleanup and remove unused code
Echap some URL parameters in FlexiAPIClient
Rename XMLRPC specific methods
Implement more FlexiSIP endpoints in the account manager
Create a new Account Creator FlexiAPI test suit
Put in common some functions of the Account Creator test suits
Complete FlexiAPIClient and the related account creator connectors
Load libjsoncpp properly
Fix response parameter in FlexiAPIClient responses
Use the new callback event system in the XMLRPC tests
Rename a few methods
Add comments to make some code more explicit
Pass jsoncpp to object
Add XCODE static/object for jsoncpp
Move the account_creator files from coreapi to src
Add a ENABLE_FLEXIAPI toggle

Reorder freeing memory when Marshalling on Native Windows ID
Add import grammar for CS

(cherry picked from commit 49592e2a)

This work required a major internal refactoring of how streams (audio, video, text, maybe others in the future) are handled by liblinphone.
This refactoring introduces a new design, where a streams are managed through a common base class named 'Stream', by a new class StreamsGroup that has the responsability of coordinating streams together.
In addition, these classes are provided with an OfferAnswerContext, that contains a representation of SDP local parameters, remote parameters, and agreed parameters.

The IceAgent has been redesigned too, renamed as IceService. It is now invoked by the StreamsGroup, and given the same OfferAnswerContext.
The IceService now supports handling of several IP addresses, using getifaddrs() (linux, android, iOS, Mac), windows to be done. The new code is more compact.

The internal function sal_stream_description_active() has been removed as its name was confusing.
Instead sal_stream_description_active() can be used to know if a stream is active (i...