Some improvement of Create user and User operation

Use User ID in User operation
Add icons to buttons in User operation
Display created user serial number in a dialog
Catch exception when creating user, close #99
Create user in background

app/build.gradle.kts

@@ -38,6 +38,10 @@ android {
                 "proguard-rules.pro"
             )
             signingConfig = signingConfigs.getByName("defaultSignature")
+            composeCompiler {
+                includeSourceInformation = false
+                includeTraceMarkers = false
+            }
         }
         debug {
             signingConfig = signingConfigs.getByName("defaultSignature")