checkpoint switching to LiteBitmaskSlots from BitIntervals.

src/main/python/Octeres/bitmask/bitmask_lite.py

src/main/python/Octeres/bitmask/bitmask_lite_spark.py

src/main/python/Octeres/data_spark.py

src/main/python/Octeres/scripts/control_bittree.py

src/main/python/Octeres/scripts/performance_run.py

src/test/python/bitmask/test_bitmask_lite.py

src/test/python/bitmask/test_bitmask_lite_spark.py

src/test/python/test_data_spark.py