Implement new url format in alerting

WIP: Dashboard & Persistent urls - Frontend Step 2

backend for new url structure.

plugins: return table with empty rows array insteaf of nil

Removes slug property in dashboard search responses since this property isn't needed
anymore and it haven't been released to any stable release.

Change the front end route for folders to /dashboards/f/<uid>/<slug of folder title>.
Use new route for deleting dashboard/folder by uid.
Retrieve dashboard/folder by uid when moving or deleting dashboards/folders.

Validates that there are only one folder/dashboard having that slug,
otherwise returns 412 Precondition Failed

WIP: Dashboard & Persistent urls - Frontend Step

If the selected folder is not in the options then manually create it. This
can happen in some edge cases (if an user has been given access to a
dashboard but does not have access to its parent folder)

Editors should be able to create dashboards in root and should be
able to create folders. They cannot administrate permissions though
and these dashboards and folders will get the default permissions.

* origin/7883_frontend_step:
  dashboards: make scripted dashboards work using the old legacy urls
  dashboards: redirect from old url used to load dashboard to new url
  dashboards: add new default frontend route for rendering a dashboard panel
  dashboards: fix links to recently viewed and starred dashboards
  dashboards: use new *url* prop from dashboard search for linking to dashboards
  dashboards: when saving dashboard redirect if url changes
  dashboards: add new default frontend route for loading a dashboard
  dashboards: return url in response to save dashboard. #7883

Allow users to change permissions inherited from root.

According to the author, the Ansible role is obsolete:
https://github.com/picotrading/ansible-grafana/issues/8#issuecomment-342210822
As the proposed alternative (https://github.com/jtyr/ansible-grafana/) hasn't been updated in the last two years either, I'm suggesting it should be removed altogether in favor of the role maintained by cloudalchemy.