Rework presence to remove online and offline virtual activities and introduce consolidated presence.

Denying a friend to subscribe presence was no more possible
once we accepted.

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.

* 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.

Add new createFriend method for LinphoneCore to avoid crash if LinphoneFriend is not link with a LinphoneCore

improve friend.find_presence_model_for_uri_or_tel, fix core.interpretUrl to normalize both phones and usernames

make sure normalized phone numbers are computed for each new subscription to take into account potentiel proxy config changes.

Add new tests.

Cherry pick c8ae2974 from master

Only alter sip_uri column in update + close/reopen connection needed after schema update + do it in transaction just in case...