Change our source reconstruction code to allow us to estimate TRFs on the brain

[cedricfoucault]

More detailed title:
Change our source reconstruction code to allow us to estimate TRFs at the subject-level in a common brain space and plot group-level estimates on the brain

In researching how to do MEG analyses in source space, I realized that we'll need the change the way in which we are doing source reconstruction so that it allows us to perform these analyses. This issue tracks the work that's needed to get there.

[cedricfoucault]

I am currently in the process of figuring out how the source reconstruction should be done and what changes are needed. Once I've figured this out, I will come up with a list of items for us to discuss and validate. Once that's been done, this issue will be broken down into actionable steps from which we can make code changes.