Adds ReaderTopics model and services.

Basic implementation that does not yet establish relationships with other models (e.g. ReaderPosts).
ReaderTopics: Better dictionary normalization. Use NSNumber for ID.
Let ReaderTopicsViewController use ReaderTopicService
Merge branch 'develop' of github.com:wordpress-mobile/WordPress-iOS into issues/1327-reader-endpoints
Merge triage.
First pass at ReaderPostService architecture.

Establishes relationships with ReaderTopic.
Does not yet remove old ReaderPost logic from the model.
Merge branch 'develop' of github.com:wordpress-mobile/WordPress-iOS into issues/1327-reader-endpoints
Removes code related to the old reader endpoints.

Updates likes, follows, reblogs, etc to use the service.
Establishes proper relationships between topics and posts.
Removes obsolete properties from ReaderPost model.
Removes obsolete code from ReaderPost model.
Updates notifications and the app delegate to call the new service.
Corrects a couple of issues marshalling values from the REST API results.
Handle html entities in site titles.
Fixes an issue with loading more posts in the reader.

Tweaks type of some contants.
Fix an issue where the no results view did not clear on first load after install.

Use derived contexts instead of the main context with the post service.
Move the save calls in the services into the performandwait blocks for clarity.
Create relationship between topics and accounts.

Cleans up topics when changing accounts
Make sure merges are performed in the background to not block the main thread.
Merge branch 'develop' of github.com:wordpress-mobile/WordPress-iOS into issues/1327-reader-endpoints
BOOLs not NSNumbers
Use NSObjects instead of NSDictionaries to represent remote REST objects.

Gets ride of the NSDictionaries used to represent ReaderTopic and ReaderPost objects to the local services.
Instead uses plain objective c objects with properties.

Also cleans up a one sided relationship between ReaderPosts and Accounts that was missed in an earlier commit.
Added REST support for blog syncing

Note that the syncBlogsForAccount: method is only called on the default
WordPress.com account, so we might as well drop XML-RPC support for it.

Refs #920 #1521

*Warning:* Jetpack sites are returned by me/sites but they won't work.
There's a bug in the API that returns the xmlrpc URLs as HTTPS, and we
don't even have the self-hosted credentials. We'll need to filter those
out until we fully support REST.
Filter out Jetpack sites from me/sites

They wouldn't work anyway since we don't have the credentials for the
site
Added analytics for when a user follows a site in the reader.
Updating version number for App Store build