WordPress Posts Widget: Self-close one <img> tag

I overlooked this when merging b7404d8175.
Check whether Jetpack is active or in development mode before loading module extras.
WordPress Post Widget: Apply 'jetpack_widget_name' filter to title

This technique should be used rather than hardcoding in the "(Jetpack)"
part of the title.
WordPress Posts Widget: Add `alt` attribute to featured images

Suggested by @jeherve.
Merge pull request #147 from kovshenin/patch-1

Don't load module-extras.php if Jetpack is not active
Jetpack: Featured Content: Prevent Featured_Content class from loading on plugin list page

Prevents the Featured_Content class from loading on the plugin list page. This allows other
plugins to load their own Featured_Content class without requiring an explicit check to
determine if Jetpack's Featured_Content class is loaded. Also ensure that class will be
the Featured_Content class that is used and Jetpack's own Featured_Content class will
automagically disable itself.
Merge branch 'master' of github.com:Automattic/jetpack