Finished CocoaLumberjacks installation/conversion

* Settled on 2.0.0-rc pod version requirement
* Created CocoaLumberjackSwift.{h,m} to expose log methods to Swift, in
  the absence of a proper Swift binding yet; .h is included in the Swift
  bridging header
* CocoaLumberjackSwift.{h,m} also sets the logging level
* Replaced all log output with DDLogSwift.log*() calls
* Added logger initialization in AppDelegate