Provide some info to users if NiftyReg segfaults

[adamltyson]

When NiftyReg segfaults, it is nearly always because of an issue relating to incorrect voxel sizes. It would be great to catch this and print something like :
Registration has failed. Please ensure that the voxel sizes you have entered are correct. Please see .... for more details

In the mean time, this can be documented .

[adamltyson]

Now documented at https://brainglobe.info/documentation/brainreg/troubleshooting.html

[adamltyson]

We could also try to warn users preemptively with something like:

• Load data
• calculate physical dimensions of the input data
• warn user if any dimension is vastly different between the atlas and the data (indicative of wrong input parameters).

The complication is that different tissue processing techniques can shrink/swell tissue quite a but, so we would have to think carefully about what "vastly" different was. I guess if it was just a warning, then the factor could be low (say 1.5x?).

cc @alessandrofelder

[alessandrofelder]

Yea, agree with your reasoning that a warning would make sense, and allow for a lower factor.