[stdlib-sig] Organizing the cookie modules

[Brett Cannon]

We have Cookie and cookielib. Neither are going away it looks like.
Combining them doesn't work as Cookie has BaseCookie and SimpleCookie
while cookielib has Cookie. Way too much confusion.

Since Cookie has to be renamed anyway thanks to its CapWords spelling,
I am proposing:

Cookie -> cookie.server
cookielib -> cookie.client

And no, I don't think every new package should have a client and
server module. =)

I realize this doesn't simplify the names and thus breaks the guiding
rule Guido gave us, but since Cookie has to be renamed anyway I am
willing to make an exception.

-Brett