Merge branch 'dopair2-vectorisation' into 'master'. Adds:
- Vectorised version of runner_dopair2_force - Expands testActivePair to include more test cases and to also test the force pair tasks - Creates a branching function for DOPAIR2 so that the corner pairs are calculated using the serial version of DOPAIR2 - pairs_all_force() now checks if particles are active before updating them - Added more macros to vector.h to improve code readability. See merge request !440