New neighbourhood features

* Added 'skipIdentical' option NeighbourhoodNearest
* Added NeighbourhoodAll
Protect against corrupt NetcdfCf files

* Properly ignore files that have a 0 time or ensemble dimension
Add 'dataset' option to SelectorMember
Properly handle missing values among configurations

* Ensure that if one configuration is missing a value, then that
  date/offset/location is not used for any of the configurations
* The case where an entire date/offset/location was missing was handled
  before.
Show perfect score in verification

* Added '-sp', which shows a line indicating the perfect score
* Added '-m ef', which shows how often the obs exceeds the forecast
* Added '-m diff', which shows the difference between FA and miss