The Python shell already allows a shell to be "dedicated" to a buffer.
This patch adds the option to create a shell dedicated to a project, as
well as the option to make all Python shells dedicated by default.

Stefan: you mentioned python.el could use project.el without a hard
dependency, so it remains compatible with old Emacsen.  Is this a good
approach?  (Also: the added seq dependency is kinda superfluous now, but
it's nice to have it available for future developments as well.)

Philip: I'm working around the possible absence of
'read-multiple-choice' here.  Not sure it's a popular/useful enough
function to include in compat, but I thought I would bring this up.