The render DAG enhancements

<p>The rendering pipeline of Terasology is represented by a direct acyclic graph (DAG) consisting of sets of <em>nodes</em> and <em>edges</em>. Nodes being (sets of) features, bearing <em>frame-buffers</em> and <em>shaders</em>. The expected semantics behind the graph's edges is communicating inter-node dependencies, which is currently not possible. The current state only defines ordering of node calls while relying on the dependencies to be hardcoded right inside the nodes themselves.</p> <p>This project sets as its goal, among others, to provide a code-base for expressing inter-node dependencies and integrating this into the current pipeline, introducing modularity. An API for game modules might be provided.</p>