lib: Update Link State Database

lib: Update Link State Database

Add new status for Vertex, Edge and Subnet to manage their
respective states in the data base.

Add new functions:
 - to register/unregister server and client
 - to show content of the Database (VTY and Json output)
 - to update and compare subnets
 - to clean vertex and ted from ORPHAN elements
 - to convert message or stream into a Link State Element and update
   Link State Database accordingly to message event

Change Edge and Vertex key computation by using the host order systematically.
This impact mostly key based on IPv4 addresses where `ntohl()` function must
be used when searching a Vertex or Edge by key.

Update the documentation accordingly

Signed-off-by: Olivier Dugeon <olivier.dugeon@orange.com>