Throw Error if Configuration Passed Into Plugin is Invalid

[kyrivanderpoel]

This should make sure that a key passed in throws an error if the plugin is not configured for it.
For instance

from oil.plugins import Plugin
class MyPlugin(Plugin):
    default_config = {
        'my_config_variable': {
            'name': 'My Config Variable',
            'description': 'A description',
            'value_description': '0 1 2',
            'default': 1,
        },
    }


config = {
    'this_is_not_valid': 'This getting passed in currently slips by'
}
plugin = Plugin(config)