BF: Make sure that subject IDs could only be interpreted as strings.
BF: Make sure that subject IDs could only be interpreted as strings.

Closes #73.

yeatmanlab/AFQ-Browser,richford/AFQ-Browser,richford/AFQ-Browser,yeatmanlab/AFQ-viz,yeatmanlab/AFQ-Browser,arokem/AFQ-Browser,richford/AFQ-viz,arokem/AFQ-Browser,richford/AFQ-viz,richford/AFQ-Browser,yeatmanlab/AFQ-Browser,arokem/AFQ-Browser,yeatmanlab/AFQ-viz