Improve navigation of Webxdc app store

If you select an app in the Webxdc app store and then press the back button, you are taken back to the chat instead of going back to the previous screen, which is unexpected and makes navigation difficult. Maybe related to this

Expected behavior

After selecting an app in the Webxdc app store, pressing the back button takes you to the previous screen showing the apps

Actual behavior

After selecting an app in the Webxdc app store, pressing the back button closes the app store and takes you to the chat