Instance counting mismatch

The instance number should be based on the number of elements with a given identifier to better mimic what FEM-Design does.

Problem

Create a model with 3 bars. 2 with identifier A and 1 with identifier B. Currently their names will be the following in our API:

A.1
A.2
B.3

But when opening the model in FEM-Design they will be renamed to

A.1
A.2
B.1 <-- 1 instead

Solution

Instead of having a private static int _barInstance field we could change it to a dictionary private static Dictionary<string, int> _barInstances.
This dictionary could map the number of instances created of each name. Like this:

{
  "A": 2,
  "B": 1
}

Testfile in testfolder 638

Start by locating the private static _barInstance field and review the test file in testfolder 638. Verify how instance names are generated for bars with repeated and different identifiers. Done means identifiers such as A produce A.1 and A.2 while a different identifier B starts at B.1, matching FEM-Design.