Make LinphoneErrorInfo a belle-sip object. Add new accessors, and make it able to take Reason headers in incoming requests (feature to be tested)

Prevent message state from going to early states if it has reached the delivered to user or displayed state.

Send 200Ok to server if message we can't decrypt to avoid useless retransmission + adaptation of tests to this behavior

Store chat message in database before file upload so that if the file upload fails we can try sending the chat message an other time.

 - Add content type information in LIME encrypted message
 - Single entry point for all types of chat messages that are first decrypted if necessary and then handled according to their content type
 - Add possibility to send chat messages with a content type that is not 'text/plain'
 - Encrypt IMDN

Fix bug where IMDN messages gets encryption by LIME and the other party then treat the decrypted message as plain text.

* 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.

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.

Added isComposing content-type to fake LinphoneChatMessage created for IM Encryption Engine incoming callback

Call IM Encryption Engine outoing & incoming callbacks also for composing messages, but do nothing with lime + test