Support for state tracing of modules and components

- DB migration scripts.
- Models: ComponentBuildTrace, ModuleBuildTrace.
- ModuleBuild.state_trace method for querying for a particular module's
state history.
- SQLAlchemy before commit session event handler for recording
module/component state changes.
- REST API verbose mode for getting state trace of a particular module.
- Tests use make_session, so that event handlers are in effect.
- Short info in README about verbose mode.
- Tests verifying whether state trace information about a module appears
in verbose mode.
- Other minor fixes (RidaBase -> MBSBase, PEP8...)

module_build_service/__init__.py

@@ -42,10 +42,10 @@ for a number of tasks:
 
 from flask import Flask, has_app_context, url_for
 from flask_sqlalchemy import SQLAlchemy
+from logging import getLogger
 
 from module_build_service.logger import init_logging
 
-from logging import getLogger
 from module_build_service.errors import (
     ValidationError, Unauthorized, UnprocessableEntity, Conflict, NotFound,
     Forbidden, json_error)