PSM: Reset 'Published Date'

Closes #4557
- The underlying issue is that the PSM is already loaded when Ember
routes from an existing post to a new post. Instead of resetting the
‘Published Date’ value manually (with jQuery), I’m using Ember’s
computed property setter to ‘refresh’ the cache for that property. I
believe that this Ember solution is better than manually going in and
resetting it with jQuery.
Create settings-menu-mixin for subview state tracking

Ref #4642
- Move duplicate code from PSM and SettingsTags to a mixin
Use CSS animations for modals

No issue

- Changes Modals to use CSS-based animations
- All modals have an animation, so the option is removed from the handlebars helper
- Removes `animation` from the handlebars helper, as all had one anyway
- Removed the `centered` style - All modals should be left-aligned
- Buttons now default to being on the left
- Cleans up some styles (modal body top spacing) which #4632 helped clean up
Provide absolute blog url in sitemap

No issue

- Adds {{blog-url}} to sitemap.xsl
- Replaces all occurences of {{blog-url}} with absolute bkog url
Tag Management: Delete Flow

Closes #4633
- The ‘delete’ button is now a smaller plain text link, opening a
confirmation modal analog to the delete user/post flow
- Adding a post count is dependent on #4654, but the modal is already a
neat step up from the immediate, warning-less deletion.
Merge pull request #4656 from felixrieseberg/iss4633

Tag Management: Delete Flow
Refactor importer with tests

refs #4605

- Move as much code as possible out of the DB API
- Split the importer into 2 concepts, code which handles different
  filetypes and code which takes the content of files and imports it into
  Ghost in some way
- Split the import process into 4 steps, load the file into a useful
  format, preprocess the data, do the import, generate a report
- Reporting is currently a no-op
- Adds a basic level of testing
Update Ember-Data.

No Issue
- ember-data@beta.12
- ember-data now warns if a payload contains properties that do
  not exist in the model.  Because of this all missing model
  attributes have been added (without their relationship defined)
  because they're currently unused and we don't need to generate
  additional API requests to resolve the async relationships.
Navigation UI Mockup

Refs #4537

Static mockup of the navigation UI

- Includes hacky JS to simulate interactions (but not dragging, which is #4540 and no modal when deleting)
- Delete & add icons have invisible padding to increase hit area
- Drag handle has the `move` cursor
- Switches into a single column at 600px and below
Add 'id' to post sort fields. So there is no longer equally sorted posts.

closes #4648
- Add id to order by fields on posts API
- Order by id on posts controller
Merge pull request #4665 from PaulAdamDavis/navigation-ui

Navigation UI Mockup
Update pg package and convert data to correct type

No Issue
- Switch 'pg.js' package for 'pg' as the native bindings are
  now an optional add-on to pg and pg.js has been deprecated.
- pg@4.1.1
- Set the driver's parser to automatically convert integer data
  returned from postgres into a javascript integer.
Merge pull request #4647 from PaulAdamDavis/modal-css-ani

Use CSS animations for modals
Merge pull request #4643 from novaugust/settings-menu-mixin

Create settings-menu-mixin for subview state tracking
Merge pull request #4563 from felixrieseberg/iss4557

PSM: Reset 'Published Date'
Merge pull request #4667 from cobbspur/sitemap

Provide absolute blog url in sitemap
Merge pull request #4671 from jaswilli/ember-data-beta12

Update Ember-Data.
Merge pull request #4676 from jaswilli/pg-update

Update pg package and convert data to correct type
Merge pull request #4646 from ErisDS/importer-refactor

Refactor importer with tests
Data importer improvements and fixes

refs #4605, #4479

- Removes versioning from the importer
- Fixes an issue with SQLITE errors not being thrown properly for posts
- Ensures that posts have a created_at date
- Makes sure that the API wrapper is properly handled