[12522] Add database changes to support more data for DB Script texts
[12523] Add const-correctness to Text related functions
[12524] Add generic DoDisplayText function and use additional data of dbscripts table

Signed-off-by: Schmoozerd <schmoozerd@cmangos.net>
[12525] EventAI: Use generic DoDisplayText and loading of additional text data
[12526] Store how many texts are loaded for validity checks. Use this with EventAI

Close cmangos/issues#202 and close cmangos/mangos-wotlk#118