on-the-fly plugin change detection and reload

[tbarron]

Currently, the crawler monitors the configuration file, detects changes, and reloads the file when it changes. We'd like it to do the same thing for plugins, so that when an updated plugin is dropped into place, the new plugin is loaded and used, rather than requiring a crawler restart to incorporate plugin changes.

[tbarron]

Currently, when the config file is updated and reloaded, the plugins are also reloaded. So the effect can be achieved by touching the config file after updating the plugin.