added common api for handling files/objects independently from their storage backend
local version of makeDirectory uses boost::fs::create_directories
ignored directories which already exist
register url schemes with the google url api
fixed S3UrlFsHandler to make use of the correct object names
Merge branch 'datacratic-internal-branch-2' into fs-backends-api
fixed s3 erasing in url handler
Merge branch 'fs-backends-api' into datacratic-internal-branch-2

Conflicts:
	service/s3.h