Add support for South African style signs

[Kelerei]

Hi,

As I'm using OsmLaneVisualizer quite frequently as a QA tool for destination mapping in ZA, support for ZA style signs would be greatly appreciated.

These are the list of changes that would need to be made (comparing to the default DE style):

• ZA drives on the left, rather than the right. There's a separate issue (issue Add support for left-hand drive #11) for this.
• Refs are generally displayed at the top of the sign instead of the bottom, and in the order in which they are tagged. The exception (for bonus points, don't worry too much about it if you don't want to): if there are multiple refs in destination:ref, multiple destinations in destination, and the count of destination and destination refs are exactly equal, the refs should be displayed next to their matching destination. (As an extreme example, see this way: the exception would apply in the forward direction but not in the backward direction!)
• destination:to data is displayed at the bottom of the sign instead of the top. Exceptions exist, but are rare enough that it's not worth bothering about.
• Sign colours: you'll actually need to look at the value of highway=* and not the value of ref=*. The rule is: unless explicitly set with destination:colour (as is currently the case), anything on highway=motorway or highway=motorway_link is blue, anything on anything else is green.
• Text colour on signs: almost always white. Refs are almost always yellow. Don't worry about the "almost" bit as the exceptions are temporary signs typically found in construction zones (those are always black text on a yellow sign), and those probably shouldn't be tagged in the first place.

If you want to see real-life examples, there's plenty of data on Mapillary (and I suppose there's Google Streetview as well, but probably not a good idea to use that as an example owing to copyright reasons). For real-life tagging examples, see both N2 relations (#963268 and #963269, although I've really only completed a small section around the M5 in Cape Town and the Mossel Bay to George motorway section. For a non-motorway example, the N9 (relations #963474 and #963473) is almost completely tagged now, though I do have further work to do there.