The offline banner notification is not cleared on wallet restart

[timbl-ont]

Description of problem

The wallet offline notification banner is not cleared on app restart. This leads to the same notification been created multiple times, once for each restart, if the phone remains offline.

Expected behavior

Only one offline notification should be displayed.

Steps to reproduce

Turn on airplane mode
Open the app (first alert)
Close the app
Re-open the app (second alert)

Screenshots and/or log output

Environment

• [ x] Occurs on Android
• [ x] Occurs on iOS

Build #: Main branch as of Sep 3

[jleach]

This needs to be tested again.