Add passcode authentification for Wifi Sharing on VLC iOS

This MR implements a user-friendly authentification mechanism on VLC iOS web server for Wifi Sharing.
Passcode authentification is enabled when VLC's passcode setting is enabled.
The user uses the passcode that he set in VLC's settings to log into Wifi Sharing.

This MR also contains :

• Cosmetic fixes on html/css, more consistent and readable indentation;
• Fixes on tvOS web pages needed after the changes on iOS web pages.