Dashboards editing UX update

[arikfr]

• Publish button will become a "top level" button, like we have it on query page.
• In "Edit Mode", there will be a consistent placeholder below all the widgets with a button to add a widget (instead of the hidden button in the menu).
• Dashboards will have two states: view mode and edit mode. In edit mode you can change layout, title, settings, etc. Basically edit mode is the combination of "Edit Dashboard" and "Edit Layout" functionalities.
• New dashboards will open in edit mode.
• The Filters toggle will be shown in a settings section below the title when you enter edit mode.