better handling of conf file loading.

[sahilseth]

If conf files cannot be loaded properly, die gracefully.

The following error is quite confusing:

library(flowr)
Loading required package: params
Loading required package: whisker
Flowr: streamlining workflows
Error : .onAttach failed in attachNamespace() for 'flowr', details:
  call: `colnames<-`(`*tmp*`, value = c("name", "value"))
  error: attempt to set 'colnames' on an object with less than two dimensions
Error: package or namespace load failed for ‘flowr’