Save token encrypted when still valid

[DylanVanAssche]

1. What happens:

   • Every start a new token is requested

2. What was expected:

   • Save the token when authenticated. Check if the token is valid and if it is on the next start we can safely use it again. If not, the login flow needs to be started.
   • User needs some kind authentication to decrypt it's token

3. How to reproduce:

   1. Launch the app
   2. Login flow appears directly

4. Environment:

   • Sailfish OS version: 2.1.0.11
   • Sailfish OS hardware: Oneplus X

[DylanVanAssche]

Waiting for the Sailfish Secrets API to add this.

[DylanVanAssche]

SFOS 2.2 will add the Sailfish Secrets API, not sure if we can use it directly might be beta.