Rename [ideal_schedule] into [ideal.schedule]

Currently we have a folder analysis/facts/model/ideal and a file ideal_schedule in folder analysis/facts/model.
For consistency, I renamed and moved this file, so now we have a file schedule in folder analysis/facts/model/ideal

analysis/definitions/task_schedule.v

 Require Export prosa.model.task.concept.
-Require Export prosa.analysis.facts.model.ideal_schedule.
+Require Export prosa.analysis.facts.model.ideal.schedule.
 
 (** Due to historical reasons this file defines the notion of a
     schedule of a task for the ideal uni-processor model. This is not