Improve Clowder tutorials

[ghost]

• [ ] Under the ‘using clowder’ tab, I have a major problem following you with these instructions: “After selecting a dataset, under the "Analysis Environment Instances", select the "Launch new instance with dataset" drop-down, select the desired tool, then the "Launch" button”. I don’t see any of these things. This absolutely needs a series of screenshots to explain what’s going on. Am I supposed to see something from the browser?
• [ ] Under ‘using clowder’, you have a dead link for “Extractor Development”
• [ ] Under ‘developing clowder extractors’, most of the links here are dead, or misdirected. Also, the whole paragraph about setting up an installation and the email server is already covered once you find the right page on the Clowder wiki.