some fixes: avoid black banners / minimize one usb related dsi exceptions / get custom banners / install shared content

[w3irDv]

This PR contains some fixes to problems I encountered when using USBLGX:

Emunand related:

• No more black animation banners due to emunand path+name being too large.
• Emunand WAD manager now installs wad's shared content. If this shared content is not previously installed in the Emunand, weird behaviour will result during loading (black screen, corrupted memory errors, ...) or when exiting (errors opening the Operations Manual, freeze when exiting, ...). This fix is already included in my previous PR.
  Other:
• Minimize probability of a DSI Exception if you move to any screen (game settings, configuration) before the USB free space is shown in the main screen. It is probably more a bypass than a definitive fix to the race condition between the async thread that computes the HD free space and the menu manager when deletes the current screen to move to a new one.
• Initial USBLGX configuration file does uses non-SSL URL to get custom banners. This is already advised in the Wii Hacks Guide. No change if the config file is already generated.

Each fix has is own commit. Any comment / code change proposal will be welcome.