Plugin: fail on setup in a way that the plugin is not available afterwards

Currently any errors on setup are caught and printed, which seems to lead to the plugin being available even if it was not installed at all, allowing for registration on a mapping and then - of course - failing on the mapping itself. This should be prevented. (true for other plugins as well)

No file or test is named. Start by tracing plugin setup error handling and the path that registers plugins for mappings; compare behavior across the plugins mentioned in the issue. Done means a setup failure leaves the plugin unavailable and prevents later mapping registration from reaching the mapping step.

Written by the indexing model from the issue text.