Refactor path lookups

Figure out all paths and file locations in one place, stash them as custom properties. -- This is the last thing I had in mind here. The approach proposed here has the advantage of handling (figuring out, looking up, creating if necessary, as and when appropriate) all paths, files or directories (I think I didn't miss any?) and things in one place, immediately after startup. If say platform-specific muckery needs to be done or whatnot, it's all in one place. Error handling is a bit of a how ya going, but a) if these things here fail, you have bigger problems :D, b) there are a couple of options I couldn't really decide between, so pick whichever is appropriate for the general flow.