Use @needs to specify task composition for paver service checks, so that arguments are bundled correctly

This reverts commit acf50c44.

This reverts commit ed80381b, reversing
changes made to 205cb8b3.

This will be a backwards-compatible change, which will allow
developers that use older versions of firefox (e.g., 28) to
continue with development while also supporting a build system
and development that uses newer firefox versions (e.g., 42)

TNL-4102

FEDX-121

The previous approach for handling NPM assets was
to symlink them into the static directory. This appeared
to cause trouble with the asset pipeline where the files
in question were not installed and then old versions were
picked up instead.

This change instead copies NPM libraries to a new
static directory so that the pipeline can consume them
as with any other file. This new directory is added to
.gitignore so that the files don't get accidentally
checked in.