Allow persistent data to be cleared without restarting localstack

[Clay Sweetser]

Currently the only way to "clear" all resources created in localstack is to restart the application. Since restarting localstack takes a nontrivial amount of time, it would be nice if there was a way to clear all resources without restarting.

[Waldemar Hummer]

@clay_sweetser This issue is now tracked in a new location: https://github.com/localstack/localstack/issues/166 . Please follow up and share your questions/experiences on the new issue. Thanks