General: Allow Jetpack Manage Notice

- Added 2 banners.
- Notice on the Dashboard asking the user to opt in
This notice can be dismissed
- Second notice on the Jetpack and Jetpack Setting Screen
 User can’t dismiss the notice only with a filter.
- When the user opts in option gets activated + JSON API needs to get
activated.
- Still need to work on changing the wording.
- Update so that after the user connects we update the setting to JSON
API.
manage-banner: initial style changes (breaking stuff)
General: Updated with suggestions from George

- Using option ’dismissed_manage_banner’  instead of
dismissed_jetpack_manage_banner
- use esc_attr_e instead  of _e
- moved the html out of translation string
- Use add_query_attr()
- Update to use Jetpack::admin_url()
- removed sprintf() when not needed.
- removed some debug code.
manage-banners: updated styles (still busted :D )
Wording updates to first banner.
manage-banner: many class changes
Merge branch 'manage-banner' of https://github.com/Automattic/jetpack into manage-banner

Conflicts:
	class.jetpack.php
General: Wording changes to outing banner and the success message.

props @csonnek
manage-banner: styles and classes for first banner
manage-banner: second banner styles added
manage-banner: minor style change
General: Moved the banner on Jetpack Site to a below the connect

Updated display_jetpack_manage_notice to
can_display_jetpack_manage_notice to be more clear.
The non dismissible nag can now be found in
opt_in_jetpack_manage_notice()
manage-banner: updated styles
manage-banner: fixed jumping button
manage-banner: removed commented code
manage-banner: rounding all corners!
manage-banner: fixing weird core bug thingy
Modifications to banner(s) copy and links

- changed copy on main dashboard banner to explain *why* you should
opt-in
- changed language to talk about “activating” rather than “opting-in”
- removed “dismiss” link as already can do that with the “x” (top right)
- Changed success message to include link to the plugins dashboard
JSON: add fallback to original slug approach

If we can't get the cached plugin slug, let's try to infer that from the
path to the plugin file.
Hide comment subscription box on passworded posts

Addresses issue #1139