Recovered default journal & snapshot store to default config

[Horusiath]

See #1861

• Default config journal plugin id is restored to point at in-memory journal (was none, causing an error).
• Default config snapshot store plugin id is restored to point at local file system one (was none with warning log message, which didn't cause any explicit error, but was breaking change in API behavior).

EDIT:

• All persistence specs are now running on default config settings, making sure that default journal and snapshot store have been initialized.

[Aaronontheweb]

Can we get spec coverage for this as well?

[Horusiath]

Tests for default journal and snapshot store included.

[Aaronontheweb]

Thank you sir