Sort out parallelisation branches and PRs

[gregorgorjanc]

So, we have:

• https://github.com/HighlanderLab/SIMplyBee/tree/Parallelisation was the first attempt to use parallelisation using doParallel that by default uses forking, but this proved challenging for use on HPC

• https://github.com/janaobsteter/SIMplyBee_fork/tree/onePSOCK was then the second attempt (by creating a branch from the Parallelisation branch) to address the forking issue by using PSOCK approach

• https://github.com/janaobsteter/SIMplyBee_fork/tree/Future was then the third attempt (by creating a branch from the onePSOCK branch, likely) since the Future package enables much simpler code than the PSOCK approach - also, we can simply plan if a script is run in serial/sequential or parallel mode, so looks like a no brainer.

So, we likely will want to go forwards with the Future approach. We are however not fully aware how well this works across different computers (laptops, servers, HPC, etc.) since the behaviour seems to be computer-dependent. @janaobsteter is testing this ... so we will wait to hear back and then decide how to move onwards.