Cocoa: Finish launching NSApp in glfwInit

This moves the remaining bits of NSApplication initialization into
_glfwPlatformInit.  As a side-effect of this, any command-line program
initializing GLFW will get a menu bar, which is not ideal.

If this has happened to you and a bisect led you here, please see the
GLFW_COCOA_MENUBAR init hint introduced in GLFW 3.3.

If this patch is a terrible idea, please get in touch in the 3.4 release
timeframe.

This is a replacement for 6e6805000a,
which attempts to preserve the existing menu bar creation behavior for
the 3.3-stable branch.

Fixes #1649.

docs/context.dox

@@ -84,10 +84,6 @@ objects are recommended for rendering with such contexts.
 You should still [process events](@ref events) as long as you have at least one
 window, even if none of them are visible.
 
-@macos The first time a window is created the menu bar is created.  This is not
-desirable for example when writing a command-line only application.  Menu bar
-creation can be disabled with the @ref GLFW_COCOA_MENUBAR init hint.
-
 
 @subsection context_less Windows without contexts