convert lockcontent api to http long polling

Websockets would work, but the problem with using them for this is that
each lockcontent call is a separate websocket connection. And that's an
actual TCP connection. One TCP connection per file dropped would be too
expensive. With http long polling, regular http pipelining can be used,
so it will reuse a TCP connection.

Unfortunately, at least with servant, bi-directional streams with long
polling don't result in true bidirectional full duplex communication.
Servant processes the whole client body stream before generating the server
body stream. I think it's entirely possible to do full bi-directional
communication over http, but it would need changes to servant.

And, there's no way for the client to tell if the server successfully
locked the content, since the server will keep processing the client
stream no matter what.:

So, added a new api endpoint, keeplocked. lockcontent will lock the key
for 10 minutes with retention lock, and then a call to keeplocked will
keep it locked for as long as needed. This does mean that there will
need to be a Map of locks by key, and I will probably want to add
some kind of lock identifier that lockcontent returns.

Command/P2PHttp.hs

@@ -14,10 +14,13 @@ module Command.P2PHttp where
 import Command
 import P2P.Http
 
+import qualified Network.Wai.Handler.Warp as Warp
+
 cmd :: Command
 cmd = command "p2phttp" SectionPlumbing
 	"communicate in P2P protocol over http"
 	paramNothing (withParams seek)
 
 seek :: CmdParams -> CommandSeek
-seek _ = liftIO $ P2P.Http.run
+seek ["server"] = liftIO $ Warp.run 8080 p2pHttpApp
+seek ["client"] = liftIO testClientLock