Fix .container position on navbar (reloaded)

Created by: soullivaneuh

This is a fixed and improved version of #9208.

I simply remove navbar-inner that is not needed anymore.

I also apply changes on _empty_head_panel and _head_panel templates.

I tested it with both desktop and mobile view on dashboard main page, no apparent side effect.

@jvanbaarsen @randx @Razer6 => Ready for review. 👍