Property wrappers

[ilyapuchka]

By adding @propertyDelegate to our existing auto-injection wrappers instead of

let client = Injected<Client>()

in Swift 5.1 we can write

@Injected var client: Client? = nil

Note: as of Xcode 11 beta 1 () are needed after property delegate name
UPD: Not an issue any more with refactoring of property wrappers into structs, but still requires initial nil value provided explicitly when using property wrapper (example updated) in class (not needed in structs)

UPD: = nil is not needed any more

[dchohfi]

hey @ilyapuchka, thoughts on this? I might be able to pick it and see what is left