Adds WhatsNew to Settings, displaying content from a Markdown file in project

[SuzGupta]

Closes #163

What it Does

Adds a new UPDATES section to the Settings view, with so far just a single row, What's New. When tapped, this leads to a view that displays a Markdown file showing the app changelog.

How I Tested

• Launch the application
• Tap the Settings tab icon
• Tap What's New
• Learn all about what's new in your favorite Twitter organizer!

Notes

• Because Swift's new(ish) AttributedString does not appear to support headers in Markdown, these were reformatted as emboldened text instead.
• The one unrelated change was to silence a SwiftLint trailing_newline warning.

Screenshot