Fix some cameras.xml DTD issues
Fix some cameras.xml DTD issues

There were a few issues with the DTD validation, none serious:

- The ID definition had a copy paste error
- XML DTDs are bonkers and force element order
- The Camera definition was requiring too much
- There were two or three typos

klauspost/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,anarsoul/rawspeed,anarsoul/rawspeed,anarsoul/rawspeed,darktable-org/rawspeed,klauspost/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed