Create DB Functions for our REST API v2 Endpoints

[lsulak]

As the ticket says, basically in #141 we designed the REST API v2 that is more comprehensive than the current one. But for this, not only server's endpoints must be implemented, but also underlying DB functions.

We have several DB functions already - use whatever you can from future/ dir in DB module, implement a new ones otherwise (will be more new than recycled probably).

The goal of this ticket is to implement DB functions as a preparation phase for the endpoints.

[lsulak]

obsolete, we have specific tickets instead of this general one