Jetpack Admin: Setting $instance private

Setting to private to block external access to the $instance property. By
having it set to public anything can come by and swap the object and Jetpack
could be sending data somewhere else or simply broken. This protects access.
If access to the object is required it can be reached with Jetpack_Admin::init()
Jetpack Admin: Setting @jetpack to private

Setting to private to block external access to the $jetpack property.
This protects access and ensure the proper type will always be set

Note: Access to Jetpack's methods can be done via Jetpack::init()->METHOD also
Refactored view code into a view template
Remove old todo from Jetpack_Client_Server

Removed an @todo that existed for over a year. The todo no longer applies
to how the class works.
Removing an old deprecated todo message
Removing unused variable
Whitespace
Whitespace
Heartbeat: Setting $instance private

    Setting to private to block external access to the $instance property. By
    having it set to public anything can come by and swap the object and Jetpack
    could be sending data somewhere else or simply broken. This protects access.
    If access to the object is required it can be reached with Jetpack_Heartbeat::init()
Switching sizeof() to count()

sizeof() is an alias to count(). Switching provides a slight performance gain
by eliminating a call from the stack http://us2.php.net//manual/en/function.sizeof.php