patch-detail: refactor JS code into submission.js

patch-detail: refactor JS code into submission.js

Move submission.html script code for toggling header info to a separate
submission.js file that makes the code easy to read and ready for change
in one place.

The listener is moved from the 'href' to separate, explicit click
listener.

Signed-off-by: Raxel Gutierrez <raxel@google.com>
[stephenfin: Removed existing JS href added in previous change and
             update commit message to reflect this]
Signed-off-by: Stephen Finucane <stephen@that.guru>