update xcode project template to c++11 / libc++

Signed-off-by: tgfrerer <tim@poniesandlight.co.uk>
update to latest poco headers via apothecary

fixes an issue where ofAddListener would not work because of a missing header adaption.

Signed-off-by: tgfrerer <tim@poniesandlight.co.uk>
Revert "update xcode project template to c++11 / libc++"

This reverts commit 53839534d452c71349b58054febdf2dec9544027.