The tileset JSON is not zipped when running gzip

[javagl]

The previous version of the tools contained a mechanism for some operations that caused the tileset.json to be written in zipped form when it was zipped in the input, and to be written in non-zipped form when it was not zipped in the input. (See, for example, the previous combineTilesets function).

The current state of the tools tried to emulate this behavior, by keeping track of whether the input tileset.json was zipped. This causes a bug where the tileset.json will not be zipped, even when running gzip.

To solve this: The zippedness of the input should not matter. The tools should always be able to read zipped input, but write the output in un-zipped form, unless zipping was the actual operation that should be performed. This can either be via the gzip command, or via a gzip pipeline stage.

(The (legacy) tilesOnly flag for the gzip operation has to be taken into account here, but that has already been generalized, and should be easy to handle)

[javagl]

I'll reopen this as a reminder that the legacy behavior of
if (inputWasZipped) writeZipped(output) else write(output)
is still applied in the TilesetUpgrader.

The upgrade functionality is addressed, in a far broader sense, in #5 , and this will also affect this aspect of the behavior.

[javagl]

The TilesetUpgrader has been updated in #41 and does now no longer try to track the compression status of the entries.