Fixes #5

- Added missing project.godot file
- Assigned Inventory.tscn as the main scene
- Added an icon.png file (Same sword image used on the asset store)
- Changed the value of the mouse filter to pass for the GridContainer in the Inventory scene
- The template can now be edited or launched from the project manager directly

project.godot

@@ -0,0 +1,20 @@
+; Engine configuration file.
+; It's best edited using the editor UI and not directly,
+; since the parameters that go here are not all obvious.
+;
+; Format:
+;   [section] ; section goes between []
+;   param=value ; assign values to parameters
+
+config_version=4
+
+_global_script_classes=[  ]
+_global_script_class_icons={
+
+}
+
+[application]
+
+config/name="Inventory System Example"
+run/main_scene="res://Inventory.tscn"
+config/icon="res://icon.png"