Support linking via foreign indices

[yairlenga]

As much as I can tell, sandman2 can not inspect and link tables via foreign indices. Adding this feature will greatly increase efficiency (reduced round trips, etc).

I believe possible to achieve same by creating views. However, there is a limit - when there are many tables - number of view become exponential.

As a starting point, supporting 1:1 relationships will be big step forward.

rest api tbd.