Related Posts: Allow filter by `post_format`

We have added `post_format` into the Elasticsearch index so we can how filter
by that for related posts. By default all post formats are returned however
there is now a `jetpack_relatedposts_filter_post_formats` that can be used like
so:

```php
// Only return image and gallery post formats
function jetpackme_related_post_only_images( $post_formats, $post_id ) {
	$post_formats[] = 'image';
	$post_formats[] = 'gallery';
	return $post_formats;
}
add_filter(
	'jetpack_relatedposts_filter_post_formats',
	'jetpackme_related_post_only_images'
);
```

Resolves #287
Images: Allow a filter to disable image resizing via WPCOM

Allow users to set a `jetpack_images_fit_image_url_override` filter which if
set will be used to determin the url to a resized image. This allows users to
bypass Photon / WordPress.com.

Resolves #1083
Nova Menus: use current instance to maintain object context for static function outside of class
JSON API: fix date format issue

we cannot use the getTimestamp() method because it is not supported in
PHP < 5.3.  Instead we'll use strtotime()
JSON API: fix date format issue

Instead of strtotime, we'll use date_format
This may need a rebase before we merge.
Related Posts: Bring UI in line with WordPress.com version

Some niceties / UI tweaks for related posts:

* Limit excerpts to 5 lines max (resolves #1249)
* Use UTF-8 ellipsis to prevent double encoding issue (#1282)
* Make entire excerpt clickable
Module modal: hide activate, deactivate, and configure buttons

when you do not have permissions to use these buttons
Fixes #1357
Merge pull request #1312 from xyu/fix/issue-287

Related Posts: Allow filter by `post_format`
Merge pull request #1313 from xyu/fix/issue-1083

Images: Allow a filter to disable image resizing via WPCOM
Merge pull request #1316 from michaeldcain/issue1309

Nova Menus: use current instance to maintain object context
Merge pull request #1333 from Automattic/fix/issue-1326

JSON API: fix date format issue
Merge pull request #1353 from xyu/relatedpost-tweak-ui

Related Posts: Bring UI in line with WordPress.com version
Merge pull request #1360 from jeherve/fix/modal-action-buttons-permissions

Module modal: hide activate, deactivate, and configure buttons
Rewrote Portfolio shortcode to use Output Buffer

Updated for develop readability.
Updated to use ob_end_clean();
Merge pull request #881 from Automattic/ob-start-shortcode

Rewrote shortcode to use output buffer instead of string concatination.