Move generateTextureFromMesh to TextureSource to fix a texture leak

TextureSource has a list of textures to delete (m_texture_trash) so this
provides a proper, non-hacky way to delete RTT textures. Also, the prior,
hacky way of deleting them seems to be broken (see pull request #803).

To avoid header file clutter by repeating the same long list of
arguments over and over again, store the arguments of
generateTextureFromMesh in a struct called TextureFromMeshParams.

Also fix issue #782 (Only use bilinear (and others) on item textures
when settings allow it).

src/mesh.h

@@ -69,20 +69,4 @@ void setMeshColorByNormalXYZ(scene::IMesh *mesh,
 		const video::SColor &colorY,
 		const video::SColor &colorZ);
 
-/*
-	Render a mesh to a texture.
-	Returns NULL if render-to-texture failed.
-*/
-video::ITexture *generateTextureFromMesh(scene::IMesh *mesh,
-		IrrlichtDevice *device,
-		core::dimension2d<u32> dim,
-		std::string texture_name,
-		v3f camera_position,
-		v3f camera_lookat,
-		core::CMatrix4<f32> camera_projection_matrix,
-		video::SColorf ambient_light,
-		v3f light_position,
-		video::SColorf light_color,
-		f32 light_radius);
-
 #endif