Sharing: Check if label value is set before to display it

For more details, check the original trac ticket:
http://plugins.trac.wordpress.org/ticket/1974
Accessibility: remove unnecessary title attributes

Remove title attributes when they match the anchor text
Sharing: default $title to empty

 so it doesn't break in other functions
Jetpack: Sharing: Consolidating 'Share this' message to one location
Jetpack: Sharing: Adding sanitization function
Jetpack: Sharing: Added default label for sharing on the front end
Twitter Cards: Refactor into a class for Namespace purposes and to be consistent with other Jetpack code.
Twitter Cards: Refactor into a class for Namespace purposes and to be consistent with other Jetpack code.
Merge branch 'twitter-cards-class' of ssh://github.com/Automattic/jetpack into twitter-cards-class
Twitter Cards: Add a field on the sharing screen to configure the twitter:site tag.
Also modifiable from the jetpack_twitter_cards_site_tag filter
Publicize: Add filter to set the twitter:site tag if there's only one shared connection to Twitter.
Use twitter:site tag as default fallback for the 'via' attribute.
Twitter Cards: Add fallback for creator tag to user publicize connection.
Twitter Cards: Fallback for twitter:creator to user publicize connection.
Remove 10 post restriction for related posts module
Twitter Cards: Fix fallback for twitter:site.

+ Improve Settings description.
Publicize: Improve fallback for Twitter:site card.

Choose one connection when there is more than one connection.
Twitter Cards: Publicize: Prioritize user connection.

Prioritze user connection rather than a global connection when setting the twitter:creator tag
Merge branch 'master' into module-related-posts-29patches
Related Posts Module: Cleanup URLs for related links

Prior links in related posts were to the originating post with a post_id to
redirect to in order to track click stats. This patch makes the flow
cleaner by getting rid or the redirect and cleaning up the URL so that it's
more sensical.

* RP links are set to the permalink of the target post without any params.
* On click JS extracts meta data about the click event and attaches it as
  query params to the target link. (Related post display position and
  originating post_id.)
* On the target page, upon render, the GET params are used to track CTR
  stats and post exclusions are set as a data param on the related post
  div.
* On load the target page will remove the related post meta query params
  that were added to the URL and reset history state to prevent cruft.