Code cleanup

Clean up comments and messy or unused code. Plan for minor fixes.

Add explicit DI annotation for directive factory to allow compilation.

Add initial "intro" card data to timeline describing the search term and
date range covered by the timeline.
Remove trailing whitespace
Expand README; point TimelineJS include at CDN

Expand the README. Document the JS script includes needed. Link
to the depedencies used.

Update example.html to include TimelineJS from the Knight Lab CDN
rather than the version checked in to the vendor/ directory.
Remove included copy of TimelineJS

TimelineJS works just fine hosted on Knight Lab's CDN, so remove
the vendor/ dir with its copy of TimelineJS. Users should point
to the CDN version or retrieve a copy of the latest JS from Knight's
Github page.