Enable Freshly Pressed for Jetpack Blogs

Enhanced Distribution: Add a server-side catch that will return JSON
data if ?get_freshly_pressed_data=true
-- will return the WPCOM Blog ID and Post ID (both of which are
probably accessible on the page already, but
this simplifies things and confirms that the Enhanced Distribution
module is enabled (as we wouldn't want to
Freshly Pressed a post otherwise).
CSS: avoid notices to be displayed over WP submenus
Media Extractor: avoid notices when preg_match fails

More details here:
http://wordpress.org/support/topic/non-robust-code-in-jetpack_media_meta_extractorget_images_from_html
Media Extractor: pass all variables to isset()

See #46
Jetpack: Multisite: Adding Multisite branch to Github
Jetpack: Multisite: Removed debugging preventing get_default_modules from firing
Jetpack: Multisite: Updating tests
Merge branch 'multisite' of github.com:Automattic/jetpack into multisite
Jetpack: Multisite: Updating tests to use instance instead of instantiation
Jetpack: Multisite: Updating tests
Multisite: Activate modules when new sites are created.

If Jetpack is on a single-site installation, or is not network-activated in a multisite installation, then modules get activated automatically when the plugin is activated.

In a Multisite installation where Jetpack is network-activated, though, that doesn't happen unless we trigger it inside a wpmu_new_blog callback.
Multisite: Correct module slugs used on Network Settings screen.

Previously the module slugs were derived by running the module name through a few string manipuations, but this resulted in incorrect slugs in some cases. For instance, it resulted in "shortcodeembeds" instead of "shortcodes", and "contactform" instead of "contact-form".

Because of this, the modules failed to be activated when new sites were created because the incorrect slug was passed to activate_default_modules(), and it couldn't verify that the associated module file existed.

This commit gets the canonical slugs from get_available_modules() instead. As a result, list_modules() and its associated unit test are no longer needed.
Fix merge conflict.
Jetpack: Multisite: Adding documentation
Merge branch 'multisite' of github.com:Automattic/jetpack into multisite

Conflicts:
	tests/test_class.jetpack-network.php
Jetpack: Multisite: Moved footer html out of Jetpack_Network class and into view file
Jetpack: Multisite: Added result notification on connection event
Jetpack: Multisite: Updating tests
Jetpack: Multisite: Removing deprecated test
Jetpack: Multisite: Fixing test