Memory improvement regarding Dialog objects

Fixed an issue where we were creating the Dialog object in
ShowDialogAction::Begin(), but were not deleting it in its counterpart,
ShowDialogAction::Reset().  This caused us to start to progressively eat
up more and more memory as more and more Dialog objects were left
undeleted.
Added the ability to skip not-yet-seen dialog

NOTE: This requires the common.dat in v1.0.1 of MLI to function
properly.  Don't sync to this revision until you've downloaded that
through the updater.

Added a toggle button in the options menu to enable players to opt to be
able to skip dialog that they haven't seen yet.
Merge remote-tracking branch 'official/master'

Conflicts:
	src/CaseContent/Conversation.cpp
Merge branch 'master' into arch-releases