Evaluation method for Drone Dataset

[mihaibujanca]

Related to #25
We will need to make sure that we can evaluate the dataset using the same metrics from:
https://github.com/uzh-rpg/rpg_trajectory_evaluation

Many of the features in that repository are things SLAMBench would benefit massively from, and ideally, we should get much of this integrated. I particularly like the plotting functionality.

That being said, for the purpose of this issue, we will focus on ensuring that the evaluation methods used in SLAMBench are compatible with the ones used for the challenge.