Read server keys from files or create if absent (#79)

* move server keys to config

* add server keys from files

* create server keys if key files do not exist

* validate loaded server key pair

* refactor fromString functions

* key files in /etc/opt/simplex

src/Simplex/Messaging/Server.hs

@@ -60,7 +60,7 @@ runSMPServer cfg@ServerConfig {tcpPort} = do
 
 runClient :: (MonadUnliftIO m, MonadReader Env m) => Handle -> m ()
 runClient h = do
-  keyPair <- asks serverKeyPair
+  keyPair <- asks $ serverKeyPair . config
   liftIO (runExceptT $ serverHandshake h keyPair) >>= \case
     Right th -> runClientTransport th
     Left _ -> pure ()