CE/save distance units preference

I would like to namespace the RandomRun formatters after this branch is merged (or at least after it is approved).
It may be worthwhile to annotate these methods just a little bit. If you write a comment just above one structured like so (note the two asterisks on the opening of the comment) Xcode will pick it up as documentation.

```
/** The current unit string suitable for showing independently. 
    Abbreviated forms will not be capitalized, whereas full forms will.
*/
- (NSString *)standAloneUnitString;
```