Add SwiftLint

[pjechris]

Add SwiftLint to lint code:

2. Add a step to run linter in github test workflow
3. Add swift format file with following rules (if they exist)
   • space/indentation: 4
   • max line width: 120
   • cases should not be indented
   • else and catch should go on a new line
   • return should go on a new line
   • warnings should be disallowed (aka max warning is 0)

(The rules should be adapted to make it work with current code)