Fix/settings restore value when dismissing keyboard

[tonelli-m]

Description

A few adjustments to the way keyboard behaves in settings screen, see below for details

Changes

• When dismissing the keyboard, restore value back to the currently stored value. That means if an invalid value is entered, when keyboard will dismiss the last entered valid value will be restored in the field
• Keyboard now dismisses when tapping outside of the field or when scrolling
• Now that keyboard can be dismissed without back or done button press, we can use the decimal keyboard again for iOS (previously the regular keyboard was used because iOS decimal keyboard doesn't have a done button)
• For values that should not be negative, use unsigned integers so that entering a negative value in the field triggers a validation error

Linked issues

#57

Remaining TODOs

N/A

Checklist

• Code compiles correctly on all platforms
• All pre-existing tests are passing
• If needed, new tests have been added
• Extended the README / documentation if necessary
• Added code has been documented

[nicolas-f]

Thanks for the PR