Empty peaks and/or excursion set

[cmaumet]

Hi @vsoch! This is an extension of your current PR #12, that implements:

• 1addc4f: deal with empty list of peaks: we need some sort of test on the coordinates to deal with the case when no peaks/clusters are listed (e.g. in http://neurovault.org/collections/1404/fsl_ds005_sub-01.nidm)
• dfcd645: check if the excursion set is empty and if so remove it form the list of images to be displayed.

Do you know if there is a way to change the message displayed in the table when the peaks structure is empty to say "No significant voxels." instead of "No matchingf record found."?

[vsoch]

Cool! I will merge this to test on my branch.