SimpleStepSelectorBuilder case when there is only one step

[leolara]

The SimpleStepSelectorBuilder creates a column for each step type, that gets to be 1 in the row where a step instance of that type starts.

When there is only one step type we don't need any column, because all steps are of this step type.

Make SimpleStepSelectorBuilder to don't add any columns where there is a column, and create a StepSelector that works without any column.

[000wan]

Hi, may I work on this issue?

[leolara]

assigned @000wan