Don't feed badRequest, notFound with request

The request parameter, in fact, was not used by such functions.
Use notFound() in servePath__()
router.js: cosmetics and style changes, cleanup

In particular, removed formatJSON() that was not used.
router.js: increase checkParameters() transparency
router.js: cosmetics

- Deploy more blank lines

- Use ALL_UPPERCASE for global variables
router: less error-prone static paths definition
router.js: the month may or may not be prefixed by zero
router.js: cosmetics: use RE_FOO not REG_FOO
router: allow multiple data descriptor names

So we can add, e.g., a data descriptor named energy for the
visualization on which we are currently working.
Teach www/index.html to actually use the API
router: Make month and year optional