Handle missing (not NA) AIC values

Still some warnings from BASiCS...

Basic skeleton so far

Split into functions, can now actually tell how it works...

Fix spelling

Fixes #69

Checks for SpatParams caused errors if parameters weren't supplied in the right
order. Fixed by making setParams a method and reordering the update list
before setting parameters.

Fixes #66

Groups (and paths) were being simulted in alphanumeric rather than number
order. Fixed by making the Group column a factor.

Fixes #49

Fixes #64

Also remove lingering references to phenoData and featureData

Also add new BASiCS tests

Also add new BASiCS tests

Fixes #48

Fixes #48

These would sometimes error due to sampling of example dataset