Export & import storage archive (#726)

* core: import and export of chat archive

* export chat archive

* import archive, support starting chat after it is stopped

* test for maintenance mode

* test/fix archive with files

* prevent starting chat after chat database was deleted or imported

* update simplexmq

src/Simplex/Chat/Mobile.hs

@@ -54,7 +54,8 @@ mobileChatOpts =
       logAgent = False,
       chatCmd = "",
       chatCmdDelay = 3,
-      chatServerPort = Nothing
+      chatServerPort = Nothing,
+      maintenance = True
     }
 
 defaultMobileConfig :: ChatConfig