Improve display labels returned from getDiscretizedBins

[d-callan]

From veupathUtils created by d-callan: VEuPathDB/veupathUtils#35

there is a function in here called getDiscretizedBins which will return a BinList object w exact bin ranges and their display labels. we have a case where the display labels are not very reader friendly, see image below:

this is from the SAM, configured as below:

[d-callan]

the last bin there should have had a display label also to 4 signifs. whether wed like to change from 4 to 2 signifs, or report to a different number of signifs for different types of data is a separate issue. we should also check that the variable in question has an annotated display range if appropriate, and make sure were using it if so.