Introduce factory classes to instantiate storage and transaction

[brfrn169]

I think we can introduce factory classes to instantiate storage and transaction objects rather than expose the Guice dependency.

For example:

The original way to get a DistributedStorage instance, which exposes the Guice dependency:

Injector injector = Guice.createInjector(new StorageModule(new DatabaseConfig(props)));
StorageService storage = injector.getInstance(StorageService.class);

The new way to get a DistributedStorage instance:

StorageFactory factory = new StorageFactory(databaseConfig);
DistributedStorage storage = factory.getStorage();

Please take a look!

[Torch3333]

Good idea, Thank you.

[feeblefakie]

Nice! LGTM! Thank you.