plumb in LiveUpdate (WIP)

Each command that first checks preferred content (and/or required
content) and then does something that can change the sizes of
repositories needs to call prepareLiveUpdate, and plumb it through the
preferred content check and the location log update.

So far, only Command.Drop is done. Many other commands that don't need
to do this have been updated to keep working.

There may be some calls to NoLiveUpdate in places where that should be
done. All will need to be double checked.

Not currently in a compilable state.

Remote.hs

@@ -425,8 +425,8 @@ forceTrust level remotename = do
  - in the local repo, not on the remote. The process of transferring the
  - key to the remote, or removing the key from it *may* log the change
  - on the remote, but this cannot always be relied on. -}
-logStatus :: Remote -> Key -> LogStatus -> Annex ()
-logStatus remote key = logChange key (uuid remote)
+logStatus :: LiveUpdate -> Remote -> Key -> LogStatus -> Annex ()
+logStatus lu remote key = logChange lu key (uuid remote)
 
 {- Orders remotes by cost, with ones with the lowest cost grouped together. -}
 byCost :: [Remote] -> [[Remote]]