Add a config.js file to the Chrome extension

This allows the Chrome extension to be configured with hypothesisConfig.
Also moved this file and the destroy.js file into an extension
subdirectory to avoid confusion with the main app files.
Show highlights when showHighlights option is provided
Add unit tests to verify showHighlights option
Include the hypothesisConfig in the bookmarklet
Use a meta tag to signify a first run

This allows the page to notify the chrome extension via an "intent"
meta tag that the sidebar should launch in first run mode.
Merge pull request #1626 from hypothesis/show-highlights-by-default

Show highlights by default in the Chrome Extension