Adds support for router rules to Big Switch plugin

Implements: blueprint bsn-router-rules

Adds bigswitch plugin extension which adds 'rules' dictionary to router objects.
Adds validation code and database components to store router rules
Adds configuration option to plugin to set default router rules and max router rules
Adds unit tests to test all router rule functionality
Adds database migration for router rules tables

The Big Switch controller's Virtual Router implementation supports "routing rules"
which are of the form:
<source, destination, next-hop, action>
This extension aims to expose this abstraction via the Big Switch Quantum plugin.

These rules are applied at the router level, allowing tenants to control
communication between networks at a high level without requiring security policies.
(e.g. prevent servers in a publicly accessible subnet from communicating with
database servers).

Change-Id: I37a2740dca93b0a8b5111764458d39f1c2b885ce
Remove single-version-externally-managed in setup.cfg

The single-version-externally-managed flag is no longer
a config option in pbr, it is now the default behaviour
in normal setuptools.

Change-Id: I5173d78680afca534b28cefa155636d9d695b1d9
Merge "Remove single-version-externally-managed in setup.cfg"
Imported Translations from Transifex

Change-Id: I49837fb8f8771c532c2fd09d67598ad839a2f7a3
Imported Translations from Transifex

Change-Id: I9b95e89cfaf76537d98ada38fb795fbaf439c996