Move HTML parsing module from core to plugin

In 0.4.0 SourceJS got a HTML API and parsing module, that allowed to automatically cache all code examples in API storage (using phantomjs script). This was specifically done to support tools like Lego, as a showcase of what components library could give to your team.

Since Lego was just proof of concept, HTML parsing feature is not required in core, especially because it's fetching heavy dependencies like PhantomJS, we decided to move this feature to separate plugin.

If you wan't to use Lego, or similar tools, you'll be able to use it the same way as in 0.4.x and 0.5.x through plugin. HTML Sync action from navigation menu in Specs will be also moved to plugin, so if you want to use Clarify with cached examples, plugin will solve the need.