Bug#961111: add an option to specify build-only components in watch

[Yadd]

Hi,

pkg-js-tools permits to choose components to install:
 * by listing components to install in
   debian/nodejs/submodules
 * or by adding "!componentName" in
   debian/nodejs/additional_components

Then a component listed in debian/watch could be used for build only.

Cheers,
Yadd