Basic GUI client, login dialog, various comments fixes after copypaste.

client/internal/helpers/platform.go

@@ -0,0 +1,13 @@
+package helpers
+
+import "runtime"
+
+// IsMobile returns true if current platform related to mobile devices (phones, tablets).
+func IsMobile() bool {
+	switch runtime.GOOS {
+	case "android", "ios":
+		return true
+	default:
+		return false
+	}
+}