Add a static value to the `relatedposts` GET param flag

This resolves #283
Merge pull request #293 from xyu/module-related-posts-283

Add a static value to the `relatedposts` GET param flag
Add a filter for post context in related posts

`jetpack_relatedposts_filter_post_context` can now be used to filter the
post context line ('In ...', 'X Comments', etc.). This resolves #278
Merge pull request #294 from xyu/module-related-posts-278

Add a filter for post context in related posts
Omnisearch: Allow filters on get_posts.

WPML filters the get_posts call and changes it to return only posts in
the current language. By default, get_posts does not apply filters. If
we add the attribute, 'suppress_filters'=>false, we allow that filter
in WPML to work normally.

Props: WPML.org
Add a `wpml-config.xml` file.

This lets WPML recognize which of our options are strings that may need
to be translated.

A share feature option is a WP option, so to make it translatable we
need to add it to wpml-config.xml file. When plugins use get_option,
they read values from the wp_options table, WPML can filter these calls
and provide translation to the values of these options.

A greeting text option is a WP option, so to make it translatable we
need to add it to wpml-config.xml file. When plugins use get_option,
they read values from the wp_options table, WPML can filter these calls
and provide translation to the values of these options.

Props: WPML.org
Top Posts: Let WPML filter the results to the current language.

Add a new filter, `jetpack_widget_get_top_posts` that lets third-party
plugins filter the results of the top posts widget to specifically
exclude certain posts if desired.

Also adds in compatibility code (compliments of the fine folks at
WPML.org) that removes posts that aren’t in the same language as the
current ui.
Switch to strict comparison.
Pull the ifcheck wrapper around everything.

Fix some whitespace and indentation.
Let WPML translate contact form additional fields.

Contact form additional fields can't be translated because they are
created on the fly. WPML can register dynamic strings to translation
with icl_translate function.

So let’s let WPML do it! :)

Props WPML.org
Bump plugin version number
Multisite: Hides main blog from the Jetpack list

The main blog *must* be connected in order for Jetpack Multisite to be useful.
The main blog was included in the list of blogs displayed at Network Admin > Jetpack > Sites.
This let to some confusion amongst users when bulk deactivating sites and not unchecking the
main blog site. It would look like everything had been disconnected. This patch removes the
main site from the list (It *has* to be connected to see the list anyways!).

Fixes and closes 271
Merge pull request #302 from Automattic/wpml-additions

Additions for better WPML compatability
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.