Support assigning sandboxes to jobs

[chrisburr]

Add routes to the Sandbox handler

• Getting input and output sandboxes at the sane time:

GET /api/jobs/{job_id}/sandbox
{
    "Input": {pfn1: presignedurl, pfn2: presignedurl},
    "Output": {pfn1: presignedurl, pfn2: presignedurl},
}

• Get just the input or output sandboxes:

GET /api/jobs/{job_id}/sandbox/{sandbox_type}
{pfn1: presignedurl, pfn2: presignedurl}

• Assign an output sandbox (it's not currently forseen there is a need to assign input sandboxes)

PATCH "SE:SandboxSE|/S3/.../abcedfg.tar.bz2" /api/jobs/{job_id}/sandbox/output

Part of #13

[chrisburr]

@natthan-pigoux is taking a look at this

[natthan-pigoux]

Related PR: #156

[natthan-pigoux]

This issue can be closed since #156 has been merged.