Handle Constant operations in Scheduling

Right now, if the SFG contains Constants the schedulers will place them at time 0, they should be placed ALAP to prevent additional memories.

added Scheduling label

assigned to @simbj106

In !470 (closed) DontCare operations was handled in Scheduling, just like that Constant operations should be handled.

Make sure that they can be rendered in a similar way (input-styled)...

unassigned @simbj106