* removes readonly editor role

* adds viewersCanEdit setting

This enable you to allow viewers to edit/inspect
dashboards in grafana in their own browser without
allowing them to save dashboards

* remove read only editor option from all dropdowns

* migrates all read only viewers to viewers

* docs: replace readOnlyEditor with viewersCanEdit

#10181
Also added better error handling when moving dashboards to other folders

* grid: fix layout saving after panel move, #10185

* don't allow to drag fullscreen panels, #10171

without a target property on the link, the signout tab on
the preferences page returned a 404.

closes #9318