removing stale files
adding more core folks
updating overview to include two-process model
mention %matplotlib magic in mpl integration

Now that #3568 is merged, we should steer folks in that direction
mention --matplotlib flag, remove pylab references
updating shell mode - lots has been removed

but enough is still there to keep this documentation around
added more references to shell
fix cookbook URL
add label to the two-process section

there used to be a whole file which talked about the work-in-progress on
moving toward the two-process ZeroMQ model, and the qtconsole docs
reference it, but after that work was finished, the work-in-progress
docs were removed.
remove specific # of years, at @minrk's suggestion
Merge pull request #3709 from ivanov/docs-cleanup

Docs cleanup