Improved customization

[gregcotten]

Hi there! Thanks for making this.

I wanted to customize the page views a bit more so I added:

1. Modernize PageScrollState to be stored as a @StateObject, bumping requirement to iOS 14 and watchOS 7.
2. Make a PageViewSettings struct to encapsulate:

• Existing preference for switchThreshold
• Preference to dial in an "drag edge threshold" which is expressed as a ratio of the width or height of the page. The default value is 0.5, which allows the entire screen.
• Preference for changing gesture types (.standard, .simultaneous, .highPriority, AND disable drag events entirely)

3. Make a default PageViewSettings that matches the current behavior of the page view