[Eva] Moves all files related to trace partitioning into partitioning/.

Makefile

headers/header_spec.txt

src/plugins/value/partitioning/partition.ml

src/plugins/value/partitioning/partition.mli

src/plugins/value/partitioning/partitioning_index.ml

src/plugins/value/partitioning/partitioning_index.mli

src/plugins/value/partitioning/trace_partitioning.ml

src/plugins/value/partitioning/trace_partitioning.mli