TSForestItemData only loading materials on client

[DavidWyand-GG]

Issue #155 was a fix for creating billboards on a dedicated server. This came about because TSForestItemData::_getShapeInstance() is creating a shape instance and always loading the materials. While issue #155 is a good fix, it may be able to be better.

Normally when a shape instance is created the materials are only loaded on the client. TSForestItemData::_getShapeInstance() goes against this and creates the materials regardless of being on the client or server. It appears to do this so it can check if it needs to add the wind effect to the shape.

However, the wind effect should be a client side only effect and I don't believe it needs to be checked on the server. This ticket exists to look into not checking the materials on the server side, and therefore passing in isClient() into the shape creation's loadMaterials flag.