[cv6] Letter Index 1.1.0 RC 3

Fixed Bug with TMDB AddOn (and probably other).

Requires the updated Version of my Core AddOn.

XF 2.3 Version only

Forum and Category Settings are now divided into two options.
Enable indexing
Display Index

Added a Index Widget.

The indexing needs to be enabled that the widget is shown.

Updated the addon code to work with xf 2.3