Restores featured_media and attachments checks

Restores attachments check in test suite.
Add password toggle to Jetpack login view

Fixes #1108
Custom NSURLProtocol to auth fetching private site content.
Only process requests to wpcom sites
Better check for wpcom site
Adds convenience methods to reg/unreg the protocol.
Updates Simperium to Mark 0.7.4
Require https and just check wpcom domain.
Make updating regcount thread safe.
Bumps wpxmlrpc to 0.6
Merge pull request #2823 from wordpress-mobile/issues/load-private-images

Custom NSURLProtocol to auth fetching private site content.
Merging `release/4.6` to `develop`

Conflicts with:
* WordPress/Classes/ViewRelated/Notifications/Controllers/NotificationDetailsViewController.m
* WordPress/Classes/ViewRelated/Reader/CommentContentView.m
* WordPress/Classes/ViewRelated/Reader/ReaderCommentsViewController. m

Unresolved:
* WordPress/Classes/ViewRelated/Reader/ReaderCommentsViewController.m
Resolves merge conflict.
Merge pull request #2838 from wordpress-mobile/issue/merge-release-4.6-to-develop

Merging `release/4.6` to `develop`
Merge pull request #2833 from wordpress-mobile/issues/2818-repair-closing-tag

Bumps wpxmlrpc to 0.6
Merge pull request #2827 from wordpress-mobile/issue/2826-updates-simperium-framework

Updates Simperium to Mark 0.7.4
Merge pull request #2815 from wordpress-mobile/issue/1108-show-password-on-jetpack-login

Add password toggle to Jetpack login view
Merge pull request #2807 from wordpress-mobile/issues/2712-restore-featured-media-check

Restores featured_media and attachments checks
Fix date calculation to load more posts

`blog.posts` also includes pages, so let's use a fetch request with a
specific entity to calculate which post is the oldest

Fixes #2841
Adjusting spacing issue in PostService.m