Add a post tab to the main tab bar.

Tapping the tab launches the post editor in a modal view.
Draft post belongs to the current or default blog but right now its just the first blog returned from a fetch.
Also organizes some includes and removes a redundancy.
Refs #675
Don't show the post tab if there are no blogs in the app.

Hide or show the post tab depending on blogs present in the app.
Fixes an issue where the rootViewController and the tabBarController could be different instances.
Refs #675
Merge branch 'develop' of github.com:wordpress-mobile/WordPress-iOS into feature/675-new-post-tab

Conflicts:
	WordPress/Classes/WordPressAppDelegate.m
Merge branch 'develop' of github.com:wordpress-mobile/WordPress-iOS into feature/675-new-post-tab

Conflicts:
	WordPress/Classes/WordPressAppDelegate.m
Merge branch 'develop' of github.com:wordpress-mobile/WordPress-iOS into feature/675-new-post-tab

Conflicts:
	WordPress/Classes/WordPressAppDelegate.m
Always show the post tab, even in the rare case there are no blogs.

When no blogs and the post tab is tapped present the login view controller to the user.
After logging in and selecting a blog show the editor.
Moves the default blog logic out of the Blog model and keeps it in the EditPostViewController.
Saves the last edited blog's url and uses that blog for new posts.
If no saved blog default to the first one returned.
Merge branch 'develop' of github.com:wordpress-mobile/WordPress-iOS into feature/675-new-post-tab

Conflicts:
	WordPress/Classes/WordPressAppDelegate.m
#675 - Removing CTidy from this PR :)
Merge pull request #684 from wordpress-mobile/feature/675-new-post-tab

Feature/675 new post tab