If you change a webclip to fullscreen you will hide the navigator bar and the bottom bar.

Download Full WebClips from Cydia.

Now when you save a website it will appear an option to add the webclip in fullscreen.

Save a website in your springboard (webclip).

After this, go to the route /private/var/mobile/Library/WebClips and search the webclip you have saved.

You will identify the webclip for the icon that appears on the springboard. In the file called Info.plist you will see the this:

Change false for true and you will have this:

Do a respring and that's all.