Too many columns of object headings

[eAlasdair]

If a number of locos are being traced, and one despawns, then the columns that the loco occupied are filled with dummy data (headings) until a new loco spawns to take its place - this helps preserve the columns each loco occupies. However if the end loco despawns there's no need for any dummy data, as there's no later loco to fill specific columns. If there's an incident where many locos are spawned at once, and then most of them despawn, the path ends up with far too much of this data.

Secondly, the purpose of the dummy data is for it to be used as column headings, but if no loco spawns to fill that column then again the path ends up with a lot of this dummy data.

The tracer should:

• Only give those headings in columns the row before an object starts being traced there (if possible)
• Recognise when all locos for a given row have been reported and stop writing any more information