Bug 421482 - UX: No context menu!
- Moved most common actions to the top level of the context menu
- Grouped similar less common actions into three submenus: "Open with...", "Import/Export" and "Extensions". This applies to both the sidebar context menu and the toolbar gear dropdown menu.
- Generated sidebarContextMenu node dynamically from within common-nav.js
- Added Copy and Paste commands to context menu
- Modified name of Raw command to "Web Browser" and grouped it under "Open with..."
- Fixed bug where deleted items were remaining in copy/paste buffer
- Removed orion.editor contentType essentially making it accept all types of files and added excludedContentTypes attribute which excludes all image types
- Removed "prepopulate" and "postpopulate" events from dropdown.js and added a "triggered" event

--Signed-off-by: Elijah El-Haddad <elijahe@ca.ibm.com>