Ability to duplicate materials

[jake-goldsmith]

Resolves #86

Adds a button in the MaterialWidget shown in the object inspector to duplicate the current material so its properties can be changed without affecting all objects using the same material. The user is prompted to enter a name for the new material.

Edge cases checked:

• Material name already exists
• Material names are filenames so check there are no illegal characters
• Prevents file separators being added as filenames.

Other changes:

• Fixed a bug where when duplicating objects the materials ObjectMap in the PickableModelComponent and ModelComponent was assigned by reference rather than deep-copied so changing the materials on a duplicate item changed all of its duplicates materials too.

Usage:

1. To set up the scenario I have duplicated the Ship. In the MaterialWidget click "duplicate" to duplicate the material.

2 Enter the desired name:

3. The duplicate material is created with the same properties as the original material. Changes can be made to its properties which only affect the new material. The new material asset is shown in the assets widget.

Todo:

• Add automated tests. I need to do more research into how we could write good tests using this UI framework so will have to take a look into that later.

[JamesTKhan]

Tested it out and everything looks good, nice work. Thank you!