WIP: remove the current buttonbar and move its buttons to the navbar.

The bootstrap navbar gives very easy support for mobile devices. Also more vertical screen space is gained; and the navbar is fixed to the top (always visible), which is also a plus.

Currently only the Add Subscription button has been moved.
Moved the "mark all as read" button to the navbar.

Also removed CSS rules for the buttonbar (the buttonbar is going to be deleted anyway). Added a CSS rule to add margin between buttons in the navbar.
Moved the "show all entries" button to the navbar.
Moved the refresh button to the navbar.
Moved the folder dropdown to the navbar.
Fix acceptance tests.
Moved the unsubscribe button to the navbar.
Removed the buttonbar partial view.

It no longer had any content, all buttons have been moved to the navbar.
Moved all partials related to the navbar and its buttons to the views/layouts/navbar folder.
Moved user-account-related links in the navbar to a dropdown. Removed the "my feeds" link from navbar.

This way navbar fits into a screen... barely.

Something will have to be done with the "my feeds" link. Perhaps it would be better if the navbar-head link linked with the /feeds path.
Fix acceptance tests.

Removed acceptance test for the removed "my feeds" link in the navbar.

Made the dropdown with the "my account", and "logout" links option so that it only appears if a user is logged in. It's a bit redundant, because the navbar itself should not appear unless a user is logged in, but it doesn't hurt to program defensively.
Moved icon to the left of the logout link.

This way all links in the user dropdown look the same.
Fixed partial view reference in views/folders/create.json.erb

The dropdown_folder partial was referenced with its old views/feeds/buttonbar/dropdown_folder path, instead of the current views/layouts/navbar/dropdown_folder path.
Fixed acceptance tests.
Header link in the navbar leads to the feeds path instead of the root path.

It doesn't make much sense for an authenticated user to visit the root path. He will be mostly interested in the feeds path.
Minor change in dropdown caret.
The folder dropdown now looks like a normal navbar dropdown, instead of a button.

It looks vastly better in screens with small width.
Unsubscribe button looks like a regular navbar link.
Refresh button looks like a regular navbar link.
"show unread entries" button now looks like a regular navbar button.