Add diagnostics module

[tsalo]

• Visual representation for diagnostics of incoming data (e.g., plot coordinates outside brain)
• Model review
• Quality control on results
• Remove coordinates from outside of masks in kernel estimators (ALEKernel masks data after convolution #37)

[tsalo]

Idea from @angielaird: post-analysis summary information, like a breakdown of which studies/foci contribute to each cluster in the meta-analytic map. I will open a separate issue about this at some point.

[tsalo]

Given that there now is a diagnostics module, I am going to close this issue.