Grouping has a few issues

[mlissner]

I discovered some issues with how result grouping works. The implementation of groups doesn't support a few different things:

1. ngroups must be set to true. If it's not the query will crash.

2. 'group.format' cannot be set to simple. If it is, the query will crash.

3. group.main doesn't work in conjunction with group.format = simple. If it's set, the query will crash.