Introduce localisable editor strings

[Fydar]

Introduce a simple method of localising all of the strings used in the editor to make the asset more accessible to people who prefer another language.

To keep the impact of the project files minimal, it's fine if these strings are sourced from a C# script.

Because the quantity of editor strings is quite small, I could have every string be a property or method on an abstract class.

• Accept user-inputted language
• Centralise editor string sources
• Use simple localised text (using automated translation) to test implementation