Fixes for Fastlane template

[DanielOaks]

While playing with Fastlane for an upcoming blog, I ran into these issues with the current template/sample project:

• The deps step may run on a different agent to the rest of the steps, meaning dependencies may not be installed.
• swiftlint tries to run on the files in the vendor folder as well.
• Test output doesn't get saved from the testing step.

I've rewritten the template a bit to perform the bundle dep installation at the start of each step, and also to run the test output through our junit annotation plugin out of the box. In addition, I was stuck for a while on xcpretty (the default xcodebuild formatter) not playing nicely with the newest version of Xcode, so added a note there about installing xcbeautify.

Adding the beta lane is just something I've seen a fair few other projects that use Fastlane+CI do, so figured it made sense to add it and show off depends_on a bit more.

Thank you! Reach out if you want to chat about this, happy to pair! 🥳

[DanielOaks]

@dannymidnight Thanks again for the link to that Ruby template. I've re-added the deps step, and it seems to work on my end!