OBD U5 Stairs

Some long overdue improvements to the stair tool finally. Winding risers and spirals, great, been waiting a long time for these. Good. 

Could still do with an additional type for half turn stairs and quarter turn stairs that allows more than 2/3/4 runs respectively. Would be even better if we could combine winding risers with these, or at least place separate types together to make up a full stair. 

A little bug that I have found though is to do with stair height. By default I am unable to change the height by setting, as it is greyed out. I have gotten around this by editing the catalog items to allow editing of the height, but think this should be enabled by default.