move pickleshare to external

can remove and make a dependency when pickleshare installs on 3.4 (should be 0.5)
remove decorator from external
remove appnope from external

make it a dependency on OS X
remove pexpect from external

make it a dependency on non-Windows
remove simplegeneric from external

make it a dependency
install ipython[all] with pip

rather than explicit dependency installation