Fix ColumnsReversedLevel

[RobinL]

Fixing issue described in following discussino:

Question re: cll.ColumnsReversedLevel

At the moment cll.ColumnsReversedLevel("first_name", "surname").get_comparison_level("duckdb").as_dict() yields:

 'label_for_charts': 'Match on reversed cols: first_name and surname'}```

But one real-world application would be to set up:

* a first name comparison something like :
    * exact match first name
    * exact match first name to surname
    * fuzzy match first name
    * else
* a surname comparison somehting like:
    * exact match surname
    * exact match surname to first name
    * fuzzy match surname
    * else

with that in mind, in that example I think you’d want a ‘one way’ columns reversed level

i.e.

```{'sql_condition': '"first_name_l" = "surname_r"',
 'label_for_charts': 'Match on reversed cols: first_name and surname'}```

Have I got that right?  I think otherwise it’s effectively an ‘exact match full name with a reversal’, which can be used in a comparison that tries to encompass the full name (`cl.ForenameSurnameComparison`) but not if names are split out into multiple comparisons

My proposed solution would be to add a ‘symmetric’ argument to the `ColumnsReversedLevel` which by dfault is False.  If activated, it compares in both directions