temporarily use web file dialogs for mac desktop
re-enable the internal pdf viewer
remove logging message from getScrollingCompentationType
implement show callbacks: url, file, and folder
Hook up command-based menu items
Implement menu item visibility, checked, and enabled states, and dynamic labels (MRU)
Suppress extra menu separators
Simple implementation for showMessageBox (use NSAlert, detached modal)
Implement Save As using NSSavePanel
Implement Minimize (All), Zoom (All), Bring All to Front
Implement Open dialog
Revert "Implement Open dialog"

This reverts commit f43c103dd2aa45b843bf6fb6d94b068904d09068.
Implement Open dialog
move unimplemented gwt callback methods to the bottom
implement show keywboard shorcut help
impement isRetina
implement isOSXMavericks
implement fullscreen mode
set title for window when document title is available
invoke vcs refresh when main frame becomes active