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
added (no-op placeholder) addValue for enum values that includes a description
runner modifications to surface launch errors to aid debugging of problems; also removes the stfbuf invocaion by default (this can be added by the user easily enough)
added value description for run result state
fixed issues in runner found by code review
make the blocked signals clear out pending signals before unblocking
improvements in runner edge cases and usability; one extra test case
Merge branch 'datacratic-internal-branch-2' into fs-backends-api
s3 default init function
fixed s3 erasing in url handler
Merge branch 'fs-backends-api' into datacratic-internal-branch-2

Conflicts:
	service/s3.h
added ability to redirect for HTTP requests through the REST service endpoint
added ability to set headers on REST responses
Merge branch 'datacratic-internal-branch-2' of github.com:datacratic/soa into datacratic-internal-branch-3
Merge branch 'runner-improvements' into datacratic-internal-branch-3
improved thread safety and utility of generic FS api