Moved drawing of tiles out to a function of its own
Added visibility to tiles - have they been seen?
Load terrain from JSON

* Lowered the size of the field for faster loading
* added resource manager that will load all json files. Please note, every loaded item needs a type and an id.
* added getter for tcod colors from string
* added flags to terrain_floor, and added terrain_wall for testing
* updated Tile to hold more data
* field now holds the player to avoid a circular dependency between game and field - input manager now uses this properly
* rewrote draw to use draw_terrain - this gets all the data from the terrain tile type
* added an initialize function in game.py