update filenames for clearer 'submissions' roles

Paired with a refactoring in the core Betterlink library, this update is
the beginning of an effort to give more control over the user-facing
look and feel to this library.

Additionally, 'highlighting' is specific to an implementation. The role
of submissions.viewer.js is to visualize a requested submission on the
page. That may include highlighting the content, but it's not required.
Similarly, submissions.interface.js may highlight content on the page to
confirm selection submission.
update module names

Rename modules to match new file structure