Switch testing to Fastlane + add SwiftLint

[bjtitus]

This PR does two primary things:

• Switches to Fastlane from the iOS orb scripts
• Adds SwiftLint file and a fastlane lane to perform linting

More specifically:

• Moves Build and Test step to Fastlane script (the results are a bit better with CircleCI)
• Removes the Pods from KanvasCameraExample
• Switches to the Cocoapods CDN source for faster builds
• Removes the process.yml which is not needed
• Adds .swiftlint.yml for local and CI linting
• Downloads specified version of swiflint (this is the same code WordPress-iOS uses but put into a Fastlane action)
• Adds a lint fastlane lane to run linting
• Adds a step to the CI to run the linting.