Resolve RAP-404 Implements parallelization over baselines for prediction.

Implements parallelization over baselines for prediction. Ready for merging.

See https://support.astron.nl/confluence/display/FGL2IM/Replacing+%27demixing%27+actions+and+results section 1.21 for latest results.

Timings: 2 directions, 4000 and 8000 sources in each, 1 channel

Original (parallel over sources)

• 2 threads: Total NDPPP time 5.67 real 10.4 user 3.42 system
• 4 threads: Total NDPPP time 4.36 real 12.64 user 5.91 system
• 8 threads: Total NDPPP time 2.78 real 15.52 user 5.18 system

New (parallel over baselines)

• 2 threads: Total NDPPP time 3.86 real 11.31 user 0.06 system
• 4 threads: Total NDPPP time 3.36 real 17.28 user 0.24 system
• 8 threads:Total NDPPP time 2.9 real 28.67 user 0.13 system

The new implentation is still not optimal.

• need update of predict_buffer_ to include the baselines used by each thread.
• need update of addBeamToData() to only consider the baselines of each thread.
• need update of ApplyBeam class to also consider the baselines of each thread.