Lay foundation for Swift project

[benjohnde]

• Create new cross-platform project
• Use Swift 4.2
• Port basic test (mostly common group)
• Port first classes as a PoC (mostly common group)

[benjohnde]

I am currently porting parts of ZXingObjC: https://github.com/zxingify/zxingify

[benjohnde]

Won't be done in near future