Add build ordering and mem requirements for tiles via a --tile-specifier-file optional param

[tgrigsby-sc]

Still a WIP This works - verified manually with last tile build. I want to try one full build before I call this done which I will do next week.

• Added --tile-specifier-file param to make_meta_tiles.py that points to an ordering file
• Added TileSpecifier that uses the tile specifier file to dictate ordering and memory requirements of a list of tiles
• Updated enqueue_tiles to make 1 call per job to tilequeue_batch_enqueue instead of a single call.
• Updated enqueue_tiles to override every job with it's requested memory number
• Improved logging and handled TileSpecifier creation exceptions by falling back to a no-op default

[iandees]

Looks good so far.