Build Links with strings, track route setup on resource and relationships

[lgebhardt]

Revert building links with 'url_helpers' for performance reasons

Now tracking whether routes have been setup for resources and relationships in the respective objects. This allows for the efficiency of string based link generation as well as warning when a route has not been setup. This should restore the performance we lost with the url_helpers.

Also reworked way the LinkBuilder handles Engines.

Closes #1259

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[krasnoukhov]

Can we keep this option? It was useful to turn off if one knows what they are doing, so there are no annoying warnings

[lgebhardt]

That makes sense

[lgebhardt]

I've restored the setting.