Adds the ground work for geometry shaders
Expands shaderData and gfxShader to allow for more shader types
note: when building a GFXShader in source you have to call setShaderStageFile with the shaderStage and the filepath for that stage.
Once we add compute shaders this will become more apparent as compute shaders are a stage of their own and do not require vertex and pixel files whereas other shaders sometimes do.
This makes some tweaks to the engine to support this, specifically, it tweaks the hardcoded shaderpaths to defer to a pref variable, so none of the shader paths are hardcoded.
Also tweaks how post effects read in texture files, removing a bizzare filepath interpretation choice, where if the file path didn't start with "/" it forcefully appended the script's file path. This made it impossible to have images not in the same dir as the script file defining the post effect.
This was changed and the existing template's post effects tweaked for now to just add "./" to those few paths impacted, as well as the perf vars to support the non-hardcoded shader paths in the engine.
