WIP tris selection

cc @Eric89GXL @dgwakeman @agramfort 

will share a validation example soon.
What you can do is figure out which vertices were not included after the connectivity matrix is constructed, manually figure out which vertices those are connected to, and correct the connectivity matrix by adding the approrpiate rows/columns. Shouldn't be terribly slow because it's only going to be a few vertices. The coding will likely be a PITA though :)