ACL:
- defined generic model for ACLs

Context:
- Extended context.proto with ConnectionSettings
- Extended context.proto with ConfigRules specific for ACLs
Extended context.proto with Constraints for Schedule, Location, and SLAs
- created ContextPolicy to bring persistent storage of policies
- updated genproto.sh

Policy:
- added missing message to list PolicyRuleIds

Updated gRPC proto files to prevent trouble with KPI sample types in devices, also updated files related to this issue.

Device:
- Implemented Driver API with some special resources to enable retrieving endpoints from devices, interfaces, and network instances.
- Implemented special resource_keys (_connect/*) to enable AddDevice to obtain settings used to connect to remote devices (address, port, username, password, etc.)
- Implemented Emulated Driver (only for testing)
- Implemented OpenConfig Driver (missing to implement monitoring; templates for Infinera devices to be tested with other device vendors)
- Minor bugs and code improvements
- Improved test unit to enable easy testing of vendor devices and keep credentials secret.

Common:
- added ORM helper function get_related_instances
- minor modifications in ORM framework

Proto:
- field/message/enum renamings in context.proto to normalize notation

Context:
- Expanded service/database/Models.py into separate models to facilitate coding
- Completed implementation of Get/Set/List/Remove methods for Context, Topology, Device, Link, and EndPoint; also completed for relation models between topology and device/link, and ConfigModels
- Implemented test units for Get/Set/List/Remove methods for Context, Topology, Device, Link, and EndPoint
- Implemented skeleton for Get/Set/List/Remove methods for Service.
- Added Tools.py with helper methods to fimplify handling of enums between ORM and gRPC messages.

Proto:
- Minor corrections in context.proto

Common:
- Minor corrections in common.orm.backend
- Improved definition of orm.Model class with get_instances and get_references
- Extended ORM unitary tests with get_instances and get_references

Context:
- Implemented missing methods in ContextClient
- Started to implement new Context data models using ORM.
- ContextModel functional using ORM and gRPC.
- Arranged old code file placing

- Context Database API and ORM rework in progress

- Complete rework of Database API
- Integration of Database API into Context
- Improvement of API

This commit is not a final implementation, just an intermediate backup.

General changes:
- implemented data type checker class
- improved database Entity/Collection/Attributes API
- implemented grpc message parsing assertions
- integrated code coverage analyzer and reporter with code testers
- added example topology NSFNET

Common to device & context services:
- improved database context API and its tests

Context service:
- updated context proto file: added AddLink/DeleteLink RPCs, added LinkId to Link
- minor changes

Device service:
- implemented device service functionality
- improved device client
- updated genproto script
- updated device proto file: configure request becomes a Device message
- updated context proto file: operational status: added KEEP_STATUS, changed DISABLED
- moved device tests to global scripts
- extended unitary tests
- temporarily disabled integration tests