fix #186
integrated issues into unit tests and addressed #169
added missing includes for tests
test case for #163
updated testing instructions
somewhat involved fix for #163

* list_resource_configs / add_resource_config are now methods of the session
* resource_configs are stored in MongoDB and kept consisten accross active components
prevent tests from executing twice
fix for #147
fixes #197
fix for #187
Merge branch 'devel' into feature/credentials
revamp security credentials

Session now inherits saga.Session, credential was renamed to context, and inherits from saga.Context.
This solves the X509 support, and all other contexts types are also available now.
Credentials are not serialized into mongodb anymore.  Resource configs are also directly communicated to the worker threads and processes, which should clear the path for closing #163.