- new property "display_name_gui" to set custom name in the backpack GUI

- fixed error on closing inventories https://github.com/PluginBugs/Issues-EpicBackpacks/issues/64
- fixed 1.8 compatibility https://github.com/PluginBugs/Issues-EpicBackpacks/issues/62
- fixed losing backpack by pressing F in some cases https://github.com/PluginBugs/Issues-EpicBackpacks/issues/57
- fixed disable_drop_backpacks not working on death https://github.com/PluginBugs/Issues-EpicBackpacks/issues/56