Plinth needs to know when installing apps is impossible

Created by: mray

I just got that motification via plinth:

Error installing application: Error during installation E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable) E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?

And it is right: I am trying to upgrade my FreedomBox right now, so actually it is no wonder that installing a new app does not work. But instead of trying and failing plinth should know from the start and do one of those things:

1. Gray out installation options with the reason
2. Display a permanent notification during the time of an upgrade
3. Immediatly pop up an easy to understand message like "FreedomBox is currently busy updating itself ... please try again in a couple of minutes."