Save meta title and meta desc on post save

Closes #4369
- Renamed `editor-route-base` -> `editor-base-route` to bring it in alignment with the view and controller mixins
- Consolidated editor route code into editor-base-route
- Removed `serialize` from EditorEditRoute, as it reimplemented the ember default
Use nested output style for Sass

References #4389

As a result of https://github.com/TryGhost/Ghost/pull/4389#issuecomment-61637323 the best way to keep everything working nicely is to use the `nested` outputStyle for now.
Create Tags Management Stubs for Ember

closes #4260

- Adds "tags" route inside of the settings routes.
- Adds this route to router.js
- Links the route from the settings.hbs template
- Adds demo tags html in tag.hbs template
- Adds flag for tagsUI
Merge pull request #4385 from novaugust/save-meta

Save meta title and meta desc on post save
Merge pull request #4273 from cobbspur/tags

Create Tags Management Stubs for Ember
Merge pull request #4393 from PaulAdamDavis/sass-nested

Use nested output style for Sass
Update to Ember 1.8.1.

http://emberjs.com/blog/2014/11/04/ember-1-8-1-released.html
Merge pull request #4399 from rwjblue/update-to-1-8-1

Update to Ember 1.8.1.
Correct logError to log err which has undefined `message`

closes #4384
 - if err is `object` && `err.message` isNOT `string`, let err = `An unknown error occurred.`
Merge pull request #4384 from meowtec/fix-error-log

fix bug in which `logError` could not resolve an err without `message`
Remove hash after the url when clicking Meta Data

Removes that hash appended to the URL when clicking Meta Data in post settings.

Closes #4386

When clicking 'Meta Data' the click event appends a # to the URL. I replaced the a with a button element so that won't happen anymore. The button has a type attribute because it will try and submit the form without it. Added text-align: left to the navlist button because the button centers it's content by default.
Merge pull request #4405 from jillesme/iss-4386

Removes hash after the url when clicking Meta Data
Adds SIGTERM handling

closes #4403
- adds SIGTERM handler to match SIGINT handler
Merge pull request #4404 from Haegin/add-sigterm-handler

Adds SIGTERM handling
Merge branch 'master' of https://github.com/TryGhost/Ghost

Conflicts:
	core/client/templates/post-settings-menu.hbs
	core/client/templates/settings.hbs