Fixes an issue where the navbar would appear when full screen is wanted.

If the linkHelper was the firstResponder, an orientation change would cause the navbar to reappear when it should be hidden.
Refs #366.
Hide link helper's title and description for landscape iPhones.

For iPhones, don't show the link form's title and description fields when in landscape orientation and not using an external keyboard.
Fixes #366.
Improves WPAlertView UITextField behavior.

Improvements affecting the link helper in the post editor and the custom image size dialog:
Make the keyboard for text show a "Next" button, tapping/pressing enter should jump to URL
Make the keyboard for URL show a "Done" button, tapping/pressing enter should insert the link

Affecting the link helper:
Select URL field by default if the link helper is launched with selected text

Fixes #367
Merge branch 'develop' of https://github.com/wordpress-mobile/WordPress-iOS into issues/366-improve-linkhelper
Use UIInterfaceOrientationIsLandscape instead of UIDeviceOrientationIsLandscape
Merge pull request #576 from wordpress-mobile/issues/366-improve-linkhelper

Issues/366 improve linkhelper