Variable Size Local Map

This pull request as of thus far is mostly intended for me to get some input from the other guys on the project as it's not completely finished; as the commit message describes I don't have custom markers functioning yet.

Eventually this is intended to resolve http://bugs.openmw.org/issues/1537

My first question is more of a generic MyGUI question, but as far as the door markers goes, what would be the best way to group door markers by their parent cell? Essentially I want to make door markers relative to some larger UI object that's invisible so that I just need to translate said object around rather than individually translating each door marker. This is because of how the current door marker code simply clears off all existing markers and repopulates all of those that the player can see on the map, which for larger local map sizes this can induce a significantly longer cell transition time. I noted this on a 20x20 local map where walking around near Balmora can induce an extra 5 or 6 seconds of cell transition time.

Secondly, the thing operates on a preference value. I wasn't sure where to stick it (right now it needs to be grouped under "Windows" and I'm unsure of if there's a preferred location). The other associated problem is that I'm not entirely sure where in the codebase I can add it to the default settings so that it will start off with a value of 3.