Add support for NSNonactivatingPanelMask

We now subclass NSPanel, which doesn't seem make any difference other than allowing for NSNonactivatingPanelMask if we want activating the menubar window to not activate the rest of the application.
Ability to override method that draws the icon

There may be more states that need to be drawn for subclassers.
Support right clicking the status item
Maintain highlight while window is open and attached

This is more consistent with other menubar item behaviors.
Prevent frame change when changing style mask

The NSWindow implementation will attempt to adjust the frame based on its assumed titlebar height. We must stop this from happening.
Make changes to attached state smoother

When programmatically changing the attached state, the window would needlessly move vertically before.
Add ability to drag window before it is active

We needed to create a custom class for the toolbar view to get the standard system behavior.
Declare some properties as nonatomic

There was no reason they should be implicitly atomic.
Don’t draw noise pattern on Yosemite

Since only the 10.10 SDK includes the AppKit version number for 10.9, it is included here if not already defined.
Draw the correct highlight background behind icon

This ensures it looks right Yosemite as well.