updated ofxiOS to use shared_ptr

also found ofPtr still being used in ofVideoPlayer and changed it to
shared_ptr.
Merge pull request #3071 from julapy/ios_shared_ptr_update

updated ofxiOS to use shared_ptr
updated TARGET_OF_IPHONE guard to TARGET_OF_IOS

ofOpenALSoundPlayer was still using TARGET_OF_IOS guard which is
deprecated,
have updated to TARGET_OF_IOS.
Merge pull request #3072 from julapy/ios_targets

updated TARGET_OF_IPHONE guard to TARGET_OF_IOS
remove glGetString that can return NULL

closes #2824