recipetool: create: support node.js code outside of npm

If you have your own node.js application you may not publish it (or at
least not immediately) in an npm registry - it might just be in a
repository on github or on your local machine. Add support to recipetool
create for creating recipes to build such applications - extract their
dependencies, fetch them, and add corresponding npm:// URLs to SRC_URI,
and ensure that LICENSE / LIC_FILES_CHKSUM are updated to match. For
example, you can now run:

  recipetool create https://github.com/diversario/node-ssdp



(I had to borrow some code from bitbake/lib/bb/fetch2/npm.py to
implement this functionality; this should be refactored out but now
isn't the time to do that refactoring.)

Part of the fix for [YOCTO #9537].

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>