Fastlane action

[dral3x]

StringsLint needs to parse all files inside a project and it can take a while to do it.

Having it running inside a Run Build Script could not be viable all the time but maybe having it in a fastlane lane (as prerequisite for building the app for a release) makes more sense.

We need to create a fastlane action so the linter can be configured and invoked in a fastlane lane.