reject on fail, bit of logging
reject on fail with 500
always fetch token for dfs
don't log here
Reject if file could not be fetched
pass auth around
add some descriptions
Merge pull request #34 from Wikia/MOB-1409

Mob 1409
Merge branch 'master' into MOB-1397

Conflicts:
	lib/addTileSet.js
	lib/dfs.js
	lib/fetchImage.js