Use packrat for reducing memory footprint

[Mirroar]

This mostly plays into #22. I've already started improving the memory footprint of room position serialization. In the end, we could save a lot more memory by switching to something like https://github.com/bencbartlett/screeps-packrat and use it across the codebase. That'll be a lot of work, and I'm not sure we can make everything backward compatible.

[Mirroar]

Some parts have now been converted, like obstacle lists in room intel. This saves quire a bit of memory already. Another great target is probably the room planner's planned locations.