Allows custom sorting for termine yarpnarap

[fgrsnau]

This PR changes the code to let the PostgreSQL database do the sorting.

[Merovius]

Personally, I'd prefer to implement the different sorting strategies in Go code, instead of assembling postgres queries. It would lead to (IMO) more readable code. Here's an example of how that could be done in Go: https://play.golang.org/p/Cjj-K_rDkAF

[Merovius]

(or alternatively, using sort.Slice: https://play.golang.org/p/XObO1DViuLm)

(or, yet another way: https://play.golang.org/p/w05YKxnwJfy)

There are a million ways, which one is the "nicest" is up to preference I guess :)

[fgrsnau]

@Merovius I updated the PR to use Sort.Slice now.