Allow default split term. Such as AND or OR, so you don't have to enter it each time.

For instance, when setting the `defaultSplitTerm` to `AND`, you can reduce the following query in length:

```
a AND b AND c
```

Becomes:

```
a b c 
```

This makes it significantly easy to create long query patterns. When using `OR` for instance:

```
danger AND (apple samsung google intel)
```
