Added initial support for alpha channel (in combine, decompose and blend nodes). Textures with alpha channels can be exported using the material node albedo input.
Updated node editor with a simple editor for enumerated parameters.
Updated all nodes so parameters are located in a "parameters" variable.
Started writing a generic node model whose behavior is defined in a json file. Should be able to replace all generators so far.
Wrote json files for bricks and noise nodes.
Started preparing a custom node.
