Add 'active' and 'voided' param_keys to RemoteLRS query_statements

[pzingg]

I was trying out TinCanPython with the Learning Locker LRS backend. I wanted to search for non-voided statements prior to a date using 'until'. However, the query_statements function returns voided as well as un-voided statements. I'm not sure about ALL LRSes, but at least Learning Locker supports queries for 'voided' and 'active" statements.

There is a bug in Learning Locker's handling of multiple query parameters (but that's an issue for their project, not TinCanPython). I tested adding 'voided' to the allowed param_keys and then querying for 'voided': False, and it does the right thing.