Skip plugin run on missing manifest.json file

[gentlementlegen]

The kernel should skip plugins that do not serve a manifest as they should be considered invalid.

          > @rndquu The issue was that the `hello-world` plugin would not serve the manifest, so the kernel would not be able to filter out the commands. I added a manifest and serve it, which should solve the problem. Also I merged in PR #75 within this one because it was needed to properly filter out the commands anyway.

If plugin doesn't serve manifest at all then what's going to happen? Perhaps we should create a new github issue for showing empty manifest related error and stopping plugin execution?

Originally posted by @rndquu in #74 (comment)

[ubiquibot]

@gentlementlegen, You are not allowed to add Time: <1 Hour

[ubiquibot]

! No permission to set labels

[gentlementlegen]

I think this is covered by #80 and now when a manifest is not found, no run happens because the manifest should describe which events the plugin will react to.

[ubiquity-os]

# Issue was not closed as completed. Skipping.