[CM-997] Add linter rules and fix warnings

[mpospese]

Introduction

Our style guide requires the use of implicit return and our library team requires full documentation, so we should add linter rules to enforce these things instead of having to spot them during code review.

Purpose

Update SwiftLint config with implicit_return and missing_docs rules. Fix any linter violations.

Scope

• Update .swiftlint.yml
• Fix linter violations

Discussion

YComponentBrowser had multiple violations of the implicit_return rule.

We want to roll out these changes to all of our YML libraries, both in Bitbucket and on GitHub.

Fixes Issue #49

📈 Coverage

Unchanged. And documentation coverage should now be enforced by the linter!