enhanced SceneToolBar tool handling (remove and insert at specific point)
added ModeButton specialisation of PushButton for use in SceneToolMode
allow externally supplied ModeButtons in SceneToolMode
renamed getElementMask to getVisibilityMask
added edit mode button to scene toolbar
Fix for issue #2051.  Not perfect (can get into a lock in some situations) but usable.
added edit modes for exteriors
Merge branch 'mode'

Conflicts:
	apps/opencs/view/render/pagedworldspacewidget.cpp
	apps/opencs/view/render/worldspacewidget.cpp
	apps/opencs/view/render/worldspacewidget.hpp
use placeholder icons in OpenCS when no proper icon is available
make [ a whitespace character in scripts (Fixes #2126)
Fix bsatool help typo
Set up ESMReader indices in OpenCS (fixes wrong terrain textures when multiple content files are loaded)