GitLab

* Introduction of LinphoneFactory singleton class to create
  core-independent object like LinphoneAddress or LinphoneVcard.
* Make several C structures inherite from belle_sip_object_t class:
	* LinphoneCore
	* LinphoneVcard
	* LinphoneAuthInfo
* Creation of the LinphoneCoreCbs class that enable to store the
  callbacks used by LinphoneCore.

Fix bug 0001391: An incorrect presence activity is added if not is contained in a received presence XML.

Add the LinphoneImNotifPolicy object to configure whether to display/send IM notifications (is_composing, message delivered, message displayed).

The (is_)read field of a LinphoneChatMessage is now deprecated, the LinphoneChatMessageStateDisplayed state is used instead.

Store weak references of chat messages in the chat room to be able to returned the same LinphoneChatMessage object to the application.