CKEditor should not fail completely when an invalid plugin is configured

See the steps to reproduce and the effects from issue JIRA-101 .

This also reproduces when adding a line in the CKEditor configuration with a plugin that is not defined, such as:

config.extraPlugins = 'foo-bar';

Basically, what happens in there is that when a plugin is not available the whole editor fails to load. I would expect that it shows an error and then loads all the other plugins and keeps on going.