escapes meta title/description

closes #2663
adds unit-test
Merge pull request #2686 from iBotPeaches/unsafe_meta

escapes " in meta title/description
Ember: correct editor layout and other niggles

no issue
- Fixes the editor view so that the layout is correct
- Remove default title
- Fixes a couple of scoping issues with notifications
Added popover component

Closes #2418, #2714
Ref #2446, #2565

- Added and injected `popover` service to globally control popovers
- Added `gh-popover-button` component
- Added `popover-mixin` for popover and popover-buttons to mixin
- Added body-event-listener mixin for popover service to watch for body
  clicks with
- Post settings and post save button both now use `gh-popover`
- Added hacks to `ember-hacks.css` to make popovers work until ghost-ui
  consolidates functionality
Export backup prior to migration

Closes #847
- Added logic to export database to the `core\server\data\` folder prior
to beginning a migration.
- Factored out versioning logic from migration to prevent circular
references
Merge pull request #2840 from novaugust/popover-service

Added popover component
render html in notifications

fixes #2844
Added error link on 404 pages

closes #2298
- added hyperlink to error templates
- added class for styling hyperlinks on error pages
Merge pull request #2792 from jomahoney/2298-error-page

Added error link on 404 pages
Merge pull request #2854 from iBotPeaches/render_notifications

render html in notifications
Ember cleanup: double quotes + removed bad tag

- All HTML / Handlebars should use double quotes
- Removed a tag I meant to remove earlier
Ember cleanup: single quotes for JS

- All JS should use single quotes
Merge pull request #2841 from gotdibbs/847

Export backup prior to migration