Updated testInteractions to use new vectorised interaction functions, both using one and two vectors.

Conflicts:
	src/hydro/Gadget2/hydro_iact.h
	src/vector.h

Conflicts:
	src/kernel_hydro.h

Use intrinsics for vector operations as arithmetic overloading is not supported by the Intel compiler yet for AVX-512 vectors.

Conflicts:
	src/hydro/Gadget2/hydro_iact.h

Use intrinsics for vector operations as arithmetic overloading is not supported by the Intel compiler yet. Updated masking operations with new macros so that AVX-512 masking is supported.

Conflicts:
	src/kernel_hydro.h

Conflicts:
	src/vector.h

Use intrinsics for vector operations as arithmetic overloading is not supported by the Intel compiler yet.

Updated version number to 0.6.0 to reflect the large number of changes to the threadpool, drifts, MPI and scaling performance in the last few months.

Periodic gravity speed and accuracy improvements



See merge request !393

Threadpoolize all the things

These are all the remaining function from the list in #338. I've tested this as far as possible on my laptop, i.e. MPI and gravity *should* work.

See merge request !384

Merge branch 'threadpoolize_all_the_things' of gitlab.cosma.dur.ac.uk:swift/swiftsim into threadpoolize_all_the_things