usermanual: proofreading thanks to Rob Z. Smith
lua : make the core-visible lua state a structure

this will allow me to have more lua private data in there later
lua : move the mutex into the new lua structure
add a function to check if we have the gdk lock
lua : run all lua code in secondary threa

lua cannot block the UI thread anymore

note that lua code can still
* starve DT out of working threads
* prevent other LUA threads from working
usermanual: several updates
collect : avoid some gtk-warnings with tags
Updated Dutch translation
Merge pull request #347 from MRIG/master

Updated Dutch translation
Updated Japanese translation
Merge pull request #348 from MRIG/master

Updated Japanese translation
camera import: can now get EXIF tags for filenames (#8415)
Merge branch 'master' of https://github.com/darktable-org/darktable into importexif