Allow import of Tabs Outliner backup files with file ending .tree (instead of .json)

[danimoh]

TKTSTO does support importing Tabs Outliner backups, however it expects them to have the file ending .json, whereas Tabs Outliner saves backups with file ending .tree. Trying to import the .tree file fails with error Unsupported file type "", must be "application/json".. After renaming the file to .json, the import works fine. In order for the user to not have to rename his backup file, TKTSTO should accept the .tree file ending, too.

[ToyKeeper]

I'll have to see if I can figure out what causes this. TKTSTO doesn't even check the file extension... it checks the mimetype. So the user should be able to use any filename, any file extension.

It seems something is rejecting the .tree files, since two people have mentioned it, but it must be at the browser level or operating system level. Will need to investigate the cause of this issue.

Until that's fixed, some users may need to rename from .tree to .json.