Add support for subpaths in the codedestination

When using tal with a high amount of different templates and macros (I'm talking about millions of different templates), the code destination folder gets filled up with cache files within no time - especially if you dont want to clear the directory every 10 minutes. This slows down the filesystem access to the specific directory (depends on the environment - filesystemtype, nfs, etc.).

This patch introduces a configurable level of subpaths which are added to the phpCodeDestination to create a structure of max 32 subpaths with 0 as default to avoid impacts on existing installations.