"Economic plugin" errors not surfaced effectively

[meejah]

I have a client configured with ZKAPAuthorizer connecting to a ZKAPAuthorizer-enabled Grid.

I made the mistake of running this client from a virtualenv that didn't have ZKAPAuthorizer installed. I did not see any errors on the console nor in the "Welcome" page, instead seeing a blank server-list.

This needs more investigation, but some more-obvious errors should be surfaced to the user to alert them that there is a configuration or "successfully connecting to servers" problem.