move sidechain modelling pipelines into modelling module

doc/contributing.rst

doc/gettingstarted.rst

doc/tests/CMakeLists.txt

doc/tests/scripts/modelling_reconstruct_sidechains.py

doc/tests/scripts/modelling_sidechain_reconstructor.py

doc/tests/scripts/unittest_sidechain_reconstruction.py

doc/tests/test_doctests.py

extras/scoring_weight_training/generate_bft_chunks.py

loop/doc/structure_db.rst

modelling/doc/CMakeLists.txt

modelling/doc/index.rst

modelling/doc/loop_closing.rst

modelling/doc/pipeline.rst

modelling/doc/sidechain_reconstruction.rst

modelling/pymod/CMakeLists.txt

modelling/pymod/__init__.py

modelling/pymod/_closegaps.py

modelling/pymod/_fragger_handle.py

modelling/pymod/_pipeline.py

modelling/pymod/_reconstruct_sidechains.py