Accounting: Move flag to config and add basic test for accounting state (#284)

* Accounting: Add config flag (default to false)

Also fix bug where query function is called twice when flag is set.

* Accounting: test state update after store req

examples/v2/chat2.nim

@@ -213,9 +213,7 @@ proc processInput(rfd: AsyncFD, rng: ref BrHmacDrbgContext) {.async.} =
         echo &"{payload}"
       info "Hit store handler"
 
-    # TODO Use same flag as wakunode
-    # To be fixed here: https://github.com/status-im/nim-waku/issues/271
-    if false:
+    if conf.swap:
       node.mountSwap()
 
     await node.query(HistoryQuery(topics: @[DefaultContentTopic]), storeHandler)