Allow mixed label and non-label files

[jidanni]

We know how to turn off and on all line labels (#303).
But let's say we have a KML (or any format) file with 500 lines that we want labeled, and another 600 that we don't.

Easy, just use <name></name>, and then there will be no label. Alas, Viking will put a TRK017 on the screen in that case.

Yes, we could edit the properties, but 600 times?

Therefore Viking needs an option to simply not put the TRK017 etc. on the screen. (Idea 1).

What about the case when we have an additional 700 that we indeed wish would get automatically labeled by Viking?

In that case there needs to be some special escape character in the <name> field... Or maybe that special character (&nbsp?) could be used for an upwardly compatible way to tell Viking to not use a label. (Idea 2.)

But that would make our KML non-portable. Other programs might show some junk on the screen. Especially when sharing it to important people just at the wrong time.

So it seems Idea 1 would be best.

See also #90.