Rename lwm2m_set_objects to lwm2m_configure. Fix registration query which should use client info.

Signed-off-by: David Navarro <david.navarro@intel.com>
API Change: remove lwm2m_add_server().

For clients, all servers information are taken from the LWM2M Security and Server Objects. These objects are thus mandatory.
The lib initialization is plit in two functions:
- lwm2m_init() to create a context. Parameters are two callbacks in change of the network communication.
The first one opens a communication session with a server identified by its ID. It is the user application responsability to retrieve associated info from the Securty object it provided. The core has no need for these info.
- lwm2m_configure() for clients to specify client informations and provide objects.

lwm2m_register() starts by parsing the LWM2M Security and Server Objects to create the lwm2m_context_t::serverList and lwm2m_context_t::bootstrapServerList before registering.

Bootstrap Servers are now stored as lwm2m_server_t in the lwm2m_context_t::bootstrapServerList.

Signed-off-by: David Navarro <david.navarro@intel.com>