Adding Quota support

Quota support limit ressources by project

 o Quick Setup :

Quota is not enabled by default, unless QUOTA section
is set in API-server configuration file (/etc/contrail/api_server.conf)
Configuration files

Example : limit to 10 virtual-network per project as default

[QUOTA]
virtual-network = 10

 o Ressources limits implementation :

Project object contain a new field 'quota'
'quota' is and k,v containing the ressource limitation
per object type, reflecting the configuration file

Obviously IDL and Cassandra database do the job to make that perssistant and configurable for each project

If limit are exceeded, basically during a REST POST request
An HTTP 403 (Forbidden) will be returned containing : "quota limit (<current limit>) exceeded for resource <object type>"