fixes iron-router errors while using tinytest

The changes add support for standalone packages that are not contained within a Meteor application.

It also changes the iron-router dependency from `weak` to normal because it currently doesn't work anyway (with meteorite packages) and caused additional problems. Since we check manually if the container Meteor app or package has iron-router as dependency we don't need  weak references (iron-router will be there).

Currently the manual checks are pretty simple – it just searches for the string `iron-router` within the `.meteor/packages` and `package.js` files. But I guess it will be sufficient for the moment ;-)
Okay, I like this approach.