ST6RI-771 With `start` action, some flow connections are not rendered properly (PlantUML)

[himi]

Since start action is a standard library element having lots of features, the visualizer needed to process them, exceeding the limit of elements that can be processed, even though the SHOWLIB style is not selected. This PR fixes the issue by preventing VPath from traversing standard library elements if SHOWLIB style is not specified.

This PR also adds a style configuration to SuccessionFlowConnectionUsage to properly render it and an error message shown in cases when the visualizer still hits the element limit.

[himi]

After this fix, the example below:

package TestFlowConnection2 {
    action a0 {
        first start;
        then 
        action a01 {
            action a001 {
                out o1;
            }
            succession flow from a001.o1 to a002.i1;
            action a002 {
                in i1;
            }       
        }
    }
}

is properly rendered as:

[himi]

I noticed this limitation hard to find if it happens. I changed to show an error message when the visualizer hits the limitation. So, if `SHOWLIB' style is enabled, the example above is rendered as: