Honor usual override rules for `.thumbnailer` desktop files
Just as, for example, $XDG_CONFIG_HOME/tumbler/tumbler.rc
overrides any $XDG_CONFIG_DIRS/tumbler/tumbler.rc
file, a file in $XDG_DATA_HOME/thumbnailers/
should override any file of the same name in $XDG_DATA_DIRS/thumbnailers/
.
This way, the user could copy any external thumbnailer installed system wide to customize it without modifying installation files.
The same should of course apply between the directories $XDG_DATA_DIRS/thumbnailers/
, so that a user installation takes precedence over the system installation.
See also #52 (closed).