Refresh href in linkTo when one of the params changes

Currently `linkTo` helper is unbound when it comes to href attribute, which may be really annoying, because suddenly you pretty templates start to be full of `{{#with}}` helpers over every `linkTo`, which has the object that potentially can change.

This can be fixed rather easily by refreshing `href` attribute when one of the params changes.

This will of course not handle the case when the actual attribute, like an `id`, changes, but it will help in **most** cases. Most of the time you use `id` and most of the time `id` does not change.