The Montgomery Township Supervisors held a special work session meeting Monday night about the multi-purpose community center proposed catacorner from the municipal building at Stump and Horsham Roads.   Two consultants from the Kimmel-Bogrette architectural firm in Conshohocken rolled out a feasibility study that calls for a two-story, 39-thousand square foot facility with two gyms, a weight room, three excercise studios, locker rooms, a running track and a kitchen.   The total project cost for the proposed community center as presented is estimated to be between nine-point-nine and eleven million dollars.