Fixed connection/input/output list-selection behavior when deleting/reordering.
Fixed tab order in VariablePropertiesDialog.
Fixed root-node connections not being updated when removing a child node.
Added "Clear Control Points" to ConnectionItem right-click menu.
Use a form layout in SceneScriptDialog to align the controls.
Added MetaEventNode::mEventName.

Was using BaseNode::mLabel to hold the event name, but of course the user
is able to edit the label.
Added context menu for NodeItem, plus UI polishing.
Fixed adding a variable undo/redo.
LuaDockWidget overhaul.

LuaDockWidget now uses a QFileSystemModel to display a tree view of a game/mod
directory's media/lua/MetaGame files and folders.

A combobox lets the user choose a game/mod directory to display.
MetaEvent overhaul.  ScriptsDock, MetaEventDock gained game-directory comboboxes.

MetaEventManager now keeps a list of MetaEventInfo for each MetaEvents.lua
file it knows about.  Previously, all the events from every .lua file were
stored in one big QMap<> with event names as keys.  That didn't allow for
events from different files with the same name (although I suspect the game
won't allow for mods defining events with the same name).

MetaEventNode remembers the source .lua file the event came from.  This is
needed in case the file gets renamed/deleted.
Added missing object names for toolbars that Qt settings code complained about.
Expand the root item in ProjectTreeDock.  Decorate root in Lua & Scripts docks.
Implemented multi-type variables.

Some node parameters can accept more than one data type.  For example, a
node parameter might accept either a Door or a Window as a value.  Multiple
types are specified as a comma-separated list of type names.

EditNodeVariableDialog was overhauled to display the referenced variable
if any, as well as display an error if the referenced node or variable doesn't
exist or the type of the referenced variable is incompatible.
Fixed ScriptVariable not updating its type when the source changed.
Fixed MetaEventFile not setting MetaEventInfo::mSource.
Set lua editor's tab width to 4 chars.

TODO: insert spaces instead of tabs, allow 8-char tabs.