ConvertUnits should leave sort order

[Peter Peterson]

Rather than always marking the event list as unsorted once a unit conversion is done, it should leave the sort order alone if possible. There are three cases that need to be accounted for:

1. Unsorted - convert units and be done
2. Sorted by tof - convert units and reverse list of events if appropriate
3. Sorted by pulse - convert units and be done

ConvertUnits has two basic branches to look at which can be improved separately: ConvertQuickly and ConvertViaTOF.

Whether or not this works is easily tested by:

1. Load an event list
2. SortEvents by whatever type is appropriate
3. ConvertUnits
4. SortEvents by the same type again

If everything went according to plan, the second sort will take no time to run.

[Janik Zikovsky]

In [15219]:

Refs #3934: Refactored units to use an initialize() method and a singleToTOF() method. This was used in EventList's to directly convert TOF's without having to go through getTofs() setTofs(). This also preserves sort order.

[Peter Peterson]

In [15223]:

Only reverse if the list is already sorted by TOF. Refs #3934.

[Owen Arnold]

Works Followed the test procedure outlined. In my test cases the first sort (prior to convert units) always took >0 seconds, after conversion, the same sort was instantaneous.

[Stuart Campbell]

This ticket has been transferred to github issue ​4781