Suggested ConfiguredGraphFactory.create() enhancement

Currently you can't really create a graph with ConfiguredGraphFactory.create() you have to first create a template. To use ConfiguredGraphFactory you've already specified a properties file with the storage.backend and storage.hostname configured. It seems like it should be possible to use those values as defaults to automatically create the graph.

##### conf/gremlin-server/gremlin-server-configuration.yaml

```
...
graphs: {
ConfigurationManagementGraph: conf/janusgraph-cassandra-configurationgraph.properties
}
```

##### conf/janusgraph-cassandra-configurationgraph.properties

```
...
storage.backend=cassandrathrift
...
storage.hostname=127.0.0.1
```

Current behavior:

```
gremlin> ConfiguredGraphFactory.create("graph");
Please create a template Configuration using the
ConfigurationManagementGraph API.
```

Proposed behavior:

```
gremlin> ConfiguredGraphFactory.create("graph");
No template Configuration currently exists. Would
you like to have one created with the current defaults
shown below? [yN]
storage.backend=cassandrathrift, storage.hostname=127.0.0.1
```

Start at the ConfiguredGraphFactory.create() entry point and review conf/gremlin-server/gremlin-server-configuration.yaml and conf/janusgraph-cassandra-configurationgraph.properties. Compare the current template-required behavior with the proposed defaults and prompt, then define the expected creation flow and its tests.

Written by the indexing model from the issue text.