First draft of the Partition Exploration.

* NOTE: This commit is an intermediate one: Code compiles, but is untested.
* Generalize many parts of the TaskMappingEncoding into the MappingEncoding.
* PartitionExploration:
  * Define the PartitionMappingEncoding based on the generalized MappingEncoding.
  * Define Mutation Operators for the PartitionMappingEncoding.
  * Define a Creator Module for the PartitionMappingEncoding.