fix holes in texture rendering #15

1. support different types of texture extension modes (set on blender texture node)
2. new custom property: hx_tile - when using a tile map for a model (usually the ground) the shader bleeds inside it's own tile instead of extending outwards

Main issue: there is a shader setting that blends each texture slightly outside of itself, for a process that removes the jittering in the texture/geo that appears by default. Everything looks better with this setting on, but to avoid bleeding into empty space, we need these small adjustments, along with painting bleed into the textures manually.