properly align area icons and clickable regions on the world map
highlight area icon on mouseover
selecting current area on world map returns to map
fix previous commit f7c10d49f518b6c6b485eef8c7e9beefa83bc238
only play the ambush message if we actually have an encounter area

This fixes random ambush messages in Baldur's Gate in BG1
*UnmemorizeSpell: added an option to skip nondepleted spells
iwd2: added proper spell unmemorization / "removal"
iwd2::guispl: display bard and sorcerer spellbooks properly

they don't populate the memorized spell window, different counts and
no manual un/memorizing
OnSpellBookMemorizeSpell: index already contains the scrolling offset
iwd2: bards have sorcerer-style spellbooks
iwd2::guispl: store the spell lists globally to save lookups
TTF: close on failure
don't force redundant empty buttons
also clear button text for empty buttons
remove redundant NULL checks
introduce a separate ResRef for TextScreens to avoid conflicts

This fixes the transition to chapter 6 in BG1 where LeaveAreaLUA would
overwrite the setting from the previous IncrementChapter.
only overwrite the default store name if we have a better one
rename (Control|Window)_GetPos to GetRect and return size, too
fix encumbrance label positioning
new function GetMaxEncumbrance