Added forgotten piece of code (InsertDescription).
Decided to visitor be const (accept and visit methods operate on const
objects and are const itself).
Created separate library - ServerAPI, to allow linking in test framework.

Scons' target Server is left as program, but depends on ServerAPI.
Added simple implementation of output() and getPositionOfTuple() Server's methods.

It's greedy and naive solution.
Introduced first test case for this implementation. It covers only check
for non-empty container when something was put into it.