Adding several tests to jetpack network tests

This commit adds several unit tests to the jetpack-network
tests and updates two existing tests (one update trivially).
get_url() is tested in more depth, as its return values are
very specific and can be tested very specifically.
Minor commit to switch back to tabs after switching to spaces
Image Widget: refactor to allow conditional loading of the styles

Use the new WP_Widget class
Move enqueue function inside the widget class
Wrap in a check to see if the widget is active
Gravatar Hovercards: add check if avatars are disabled

Until now, Gravatar Hovercards scripts could be enqueued even if you didn't display any avatars on your site
Infinite Scroll: Do not enqueue all scripts on single pages

Fixes #634
Previous commit 19fd934d9d29684bd0535851fd5b2215c40af66c didn't completely fix things
Subscriptions: only enqueue the subscription form css when needed

Enqueue the css during widget output instead of using wp_enqueue_scripts
Likes: move inline js to separate file, enqueued in footer

Makes it easier to manipulate that js later on
Fixes #868
Merge pull request #971 from jeherve/update/likes-inline-js

Likes: move inline js to separate file, enqueued in footer
Merge pull request #969 from jeherve/fix/enqueues-subscription-widget

Subscriptions: only enqueue the subscription form css when needed
Merge pull request #963 from jeherve/fix/enqueues-infinite-scroll

Infinite Scroll: Do not enqueue all scripts on single pages
Merge pull request #962 from jeherve/fix/enqueues-gravatar

Gravatar Hovercards: add check if avatars are disabled
Merge pull request #961 from jeherve/fix/enqueues-image-widget

Image Widget: refactor to allow conditional loading of the styles
Likes: only enqueue Likes scripts when necessary

Move all scripts into separate function
Check if the Likes are displayed on the page before to enqueue
Likes: uncommenting filter, oops
Merge pull request #958 from jeherve/fix/enqueue-likes

Likes: only enqueue Likes scripts when necessary
Merge pull request #953 from enkrates/add-and-update-jetpack-network-tests

Adding several tests to jetpack network tests
Adds a test class covering functions.compat.php

The functions.compat.php file has two functions that parse some
specific pieces of possible YouTube urls. This commit adds a test
class that tests each kind of sanitization that youtube_sanitize_url
performs and also test the two types of urls that jetpack_get_youtube_id
returns ids from.
Carousel: Trim whitespace
Related Posts: strip HTML Tags from post title

Fixes #974
filter $privacy_checks so we don't catch any chaff

There had been a bug where some things that weren’t modules got lumped
into is_module checks through this, because of
e4dd8b392a092ce22d78468561ac6eb985f0e87f