When a snippet is submitted, but there's an error, we didn't keep the
visibility level. As the default is private, this means that submitting
a public snippet that failed would then fall back to being a private
snippet.

With new navigation design it makes no sense to duplicate title in the
header

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Add new global application settings for default project and snippet
visibility levels.

Make the following changes to deal with new behavior in Rails 4.1.2:

* Use nested resources to avoid slashes in arguments to path helpers.

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>