shell: New layout for navigation.
shell: Adapt update_global_nav to new layout.
shell: Move system information code to server page.
shell: Remove "Rescue Terminal" option from dashbord menu.
shell: Highlight active navigation tab.
shell: Save space on the server dashboard

By using the hostname and realms directly as the label of buttons for
changing them.  Also, always leave a realm via a dialog.
test: Adapt check-shutdown-restart
shell: Register dialogs separately from pages.

So that the upcoming refactoring can be done without having to bother
with dialogs.  Dialogs will get their own makeover.
shell: Make cockpit.loc private.

And refer to it as "page navigation parameters".
shell: Move URL encoding and decoding into "base" package.
shell: New-style URLs.
shell: Separate page parameters into host, path, and options.

And remove the old { page: "..." } construct from the API.