webapi/deep-manifest t=JSON: don't return the (large) manifest/SI/verifycap lists...

webapi/deep-manifest t=JSON: don't return the (large) manifest/SI/verifycap lists unless the operation has completed, to avoid the considerable CPU+memory cost of creating the JSON (for 330k dirnodes, it could take two minutes to generate 275MB of JSON). They must be paid eventually, but not on every poll