Issue-24 Xcode 13 fixes

[pankova]

Closes #24

First: Combining Xcode 13 and iOS 15 had these bugs

1. Transparent navigation bar until scroll up
2. Transparent splash screen
3. Transparent tab bar until scroll up
4. Untappable buttons and textfields in custom tableview cells

Second: The minimum supported iOS version had been increased to 13 by agreement

Testing

• Device: iPhone 12 mini, iOS15.5
• Simulator iPhone 13 mini, iOS 15.5
• Simulator iPhone 11 Pro Max, iOS 14.5
• Simulator iPhone 8, iOS 13.7

Checks

• System background color splashscreen: dark for a darkmode, white for a lightmode
• Visible nav bar after launch on all screens
• Visible tab bar after launch on all screens
• Tappable Add another button, one line and two line textfield on EditSafetyPlan screens

[eddielement]

@pankova These changes look great! I merged both pull requests, tweaked a few things, and I can push out an update now unless you wanted to finish anything else. :)