Adding support for prepending to lists.

This PR adds support for:

Adding (appending or prepending) values to a list can be accomplished by adding a new JSON-style array to an existing list column.

```sql
UPDATE plays SET players = 5, scores = scores + [ 14, 21 ] WHERE id = '123-afde';
UPDATE plays SET players = 5, scores = [ 12 ] + scores WHERE id = '123-afde';
```
Adding was working fine, but prepending wasn't.

I realize that code does not read well, but (smart) alternative would look even more counter-intutive: it'd be map over operator-or-value function which would turn operator into operator and cql-value for value  + reverse if we're in backwards order.