UI/UX: fix username and ringId appearance

Because Account View Model is created at the very beginning of app
launching, it is possible to create it when account does not exists.
This patch makes variables lazy, so all values will be rendered when
screen become visible. Also it adds name lookup, account does not have
username.

Change-Id: Ia4747bdb2efaffd8b0f39109407946e736ab09e5
Reviewed-by: Andreas Traczyk <andreas.traczyk@savoirfairelinux.com>