Miscellaneous

Some bugfixes, a small feature. See commits.

I can remove the read-only GUIs if you want, but I think this is an useful option.
There's two downside with them (not critical):
 - the content is not synchronized: I use a copy of the inventory from when it is opened, because using directly the inventory displays the animations;
 - the title is not translated if the container is not renamed (ex: `container.dispenser`), because there isn't any option to translate these strings. This can be fixed by adding the translations in the plugin directly.