[WIP] Explain Queries

Following up on #209

Adds an option to run EXPLAIN queries for all run queries (for the chosen type of queries, default = select). This will add the output of the EXPLAIN to a new query row, in the params.

![explain](https://cloud.githubusercontent.com/assets/973269/4590240/4562cd7e-505d-11e4-97ff-9a92324342fd.png)