add version command (#123)

* Add /version and /v flags

* Move version info from C Chat.Help to Chat.View

* Move version string, use it in Main startup

* use "SimpleX Chat" consistently

Co-authored-by: TheTaoOfSu <TheTaoOfSu@protonmail.com>

src/Simplex/Chat/Controller.hs

@@ -25,6 +25,9 @@ import Simplex.Messaging.Agent.Store.SQLite (SQLiteStore)
 import System.IO (Handle)
 import UnliftIO.STM
 
+versionNumber :: String
+versionNumber = "0.4.2"
+
 data ChatConfig = ChatConfig
   { agentConfig :: AgentConfig,
     dbPoolSize :: Int,