[Root] Enable onscreen navigation bar in android which is not enabled by default

To enable navigation bar :

• Your phone should have root access.
• Download the Build Prop editor from here and install it in your phone.
• Open the app and grant root access.
• In the app, touch the '+' button
• Set the property name as 'qemu.hw.mainkeys'.
• Set the property value as 0.
• Reboot your phone.
• That's all