Improved Equipment and IVariable usages

To try and make the IVariable interface more usable elsewhere we have made a few underlying convention interfaces, this should not really effect the higher level interfaces much but it gives us greater flexibility to re-use a lot of the existing infrastructure on other areas like AI etc.

Also worth noting the equipment interface has been moved over to use the variables interface under the hood so now rather than it being a bespoke object with each slot being a property, it now uses the same extension method approach to add your own flavour of equipment on top of it, making it more reusable for everyone.