Simplify pane:active-item-changed events

Panes now trigger an event every time their active item changes,
regardless of whether the pane itself is active. Panes also trigger
events when the become active and when they are removed. The rootView
now scopes its active-item-changed event listener only to active panes,
and also listens to listens to pane activation and removal events to
update the title when switching active panes and removing the last
pane.

src/app/pane.coffee

@@ -40,7 +40,7 @@ class Pane extends View
       pane.makeInactive()
     wasActive = @isActive()
     @addClass('active')
-    @trigger 'pane:active-item-changed', [@currentItem] unless wasActive
+    @trigger 'pane:became-active' unless wasActive
 
   makeInactive: ->
     @removeClass('active')
@@ -80,7 +80,7 @@ class Pane extends View
     @currentItem = item
     @currentView = view
     @currentView.show()
-    @trigger 'pane:active-item-changed', [item] if @isActive()
+    @trigger 'pane:active-item-changed', [item]
 
   addItem: (item) ->
     return if _.include(@items, item)
@@ -187,7 +187,7 @@ class Pane extends View
       sibling = parentAxis.children().detach()
       parentAxis.replaceWith(sibling)
     container.adjustPaneDimensions()
-    container.trigger 'pane:active-item-changed', [null] unless container.getActivePaneItem()
+    container.trigger 'pane:removed', [this]
 
   afterRemove: ->
     item.destroy?() for item in @getItems()

src/app/root-view.coffee

@@ -40,7 +40,9 @@ class RootView extends View
       @handleFocus(e) if document.activeElement is document.body
 
     project.on 'path-changed', => @updateTitle()
-    @on 'pane:active-item-changed', => @updateTitle()
+    @on 'pane:became-active', => @updateTitle()
+    @on 'pane:active-item-changed', '.active.pane', => @updateTitle()
+    @on 'pane:removed', => @updateTitle() unless @getActivePane()
 
     @command 'window:increase-font-size', =>
       config.set("editor.fontSize", config.get("editor.fontSize") + 1)