gulpfile: fix nodemon settings

Remove the dependency on packages, provide sensible static configuration
that works for all packages and non-packages alike.

Ignore `**/test/**` files.

Remove no longer used method `findSrc()`.

Note: as of #7, there is no `modules/package.json`, thus the previous
nodemon configuration was not picking changes made in `modules/*.js`.

/to @ritch please review

I do realise this is dismantling the structure you have built in gulpfile. My hope is that the change is for better, as it reduces amount of code to maintain.