Add initial QR Code support

QR Code scanner is based on ZXingObjC.
Shadowsocks URL scheme "ss://" is supported.
Add QR Code generator

Fix Base64 padding issue
Open unknown links in Safari
Add social sharing feature
QR Code decoding from photo library
Update localizations
Tweak several translations
Improve camera view to auto focus

Fix memory leak when generating QR Code image
Fix auto focus of camera
Backward support for iOS 5
Add new credit in readme
Add legacy support for package script