Replace StackNavigator with SwitchNavigator

[pmespresso]

Problem:

It seems before the v2.1 bump that we have been incorrectly using a StackNavigator for navigation, which was fine but with the latest version of react-navigation we had to work around it by setting key to undefined when resetting the route.

StackActions.reset({
                index: 1,
                key: undefined, // FIXME
                actions: [
                  NavigationActions.navigate({ routeName: 'AccountList' }),
                  NavigationActions.navigate({ routeName: next })
                ]
              });

Solution

The correct solution is to refactor our navigator to use a SwitchNavigator instead. react-navigation/react-navigation#1127 (comment)

IIRC I used the workaround as the refactor would be potentially quite hairy and that particular bump PR was already big and hairy enough.

[Tbaut]

it's at the following places:

https://github.com/paritytech/parity-signer/blob/e781b8c1647c79773ec0e900ff8a0092f722155c/src/screens/AccountUnlock.js#L54

https://github.com/paritytech/parity-signer/blob/e781b8c1647c79773ec0e900ff8a0092f722155c/src/screens/AccountPin.js#L77

https://github.com/paritytech/parity-signer/blob/e781b8c1647c79773ec0e900ff8a0092f722155c/src/screens/AccountPin.js#L77