Implement TISTUD-3601 Allow users to specify to be warned about missing semicolons
  - Add warnings about missing semicolons
  - Externalize UI strings
  - Allow user to select severity of missing semicolons: ignore, info, warning, error
  - Begin to unify IParseError and IProblem
  - Take severity of missing semicolons from prefs
  - Default to warning for missing semicolons