Fix segfalt in QuickKeysMenu when item is no longer in inventory

Fixes segfalt when a item allocated to a quick key is no longer in the players inventory. Issue can be reproduced by dropping a item assigned to a key then either pressing the key or moving the mouse to call the tooltip in the F1 dialog. (continued from !5 (closed), !6 (closed))

Changes:

• add name/id strings for item lookup and message boxes
• add null pointer check for ItemPtr tooltips
• add new struct to hold above + existing widget/type data (as per !6 (closed))
• change int mSelectedIndex/mActivatedIndex to pointers to struct