Make importer more robust for tags

Closes #3242

- Add checks for valid fields in tags and posts
- Add unit test with empty tag export data file
- Add unit test with empty post export data file
custom slugging capabilities for individual user pages

closes #3401
- modifying slug-generator to be more generic
- adding slugging capabilities for /settings/users/:slug
- modified posts to use the updated slug-generator
Avoids duplicate notification / transition

no ref
- Let application.js handle transition after setup
- Remove duplicate loading of server notifications
Fixing pg build.

refs #2499
- Properly reference pg client
- Fix broken sql queries
Update user roles in store after owner transfer

Closes #3466
- Transferring the owner role is now done via a separate
  endpoint and not through Ember-Data.  As a result the
  user role data needs to be updated manually.
- Updated the owner endpoint to return a response body
  containing the updated user objects.
- Updated tests.
Keyboard shortcuts for Mac vs All

Closes #3029, Ref #3469
- Editor shortcuts are now built in a separate file, which uses `ctrlOrCmd` to correctly set OS specific shortcuts.
- Removed `newLine` and `selectWord` shortcuts
Complete frontend multi-user features

closes #3076

- author RSS pages
- fixes page_url / pagination helper
- add 'author' option to has helper
- tests for author pages, author rss pages and helpers
Merge pull request #3471 from novaugust/editor-shortcuts

Keyboard shortcuts for Mac vs All
Merge pull request #3472 from morficus/issue-3401

custom slugging capabilities for individual user pages
Merge pull request #3480 from jaswilli/issue-3466

Update user roles in store after owner transfer
Merge pull request #3477 from halfdan/duplicate-notification

Avoids duplicate notification / transition
Cleanup CodeMirror shortcuts.

* Add titleize utility function.
  * Capitalizes first word.
  * Capitalizes all words not contained in simple article/conjunction
    list.
* Enable shortcuts for `uppercase`, `lowercase`, and `titlecase`.
* Fix header shortcuts
  * Ensure that header shortcuts do not duplicate text.
  * Make headers idempotent (pressing `ctrl+alt+1` then
    `ctrl+alt+2` does not make `# # # blah`.
Merge pull request #3476 from rwjblue/moar-shortcuts

Enable uppercase, lowercase, titlecase shortcuts.
Shorter notifications

Basic notifications are unnecessarily verbose and, in some instances, even cause line-wrapping to occur. This change shortens them to short, concsise statements to indicate what action has taken place.
Fix naming of export file during migration

No Issue
- The method that generates a filename for the export during
  a migration returns a promise, not the filename directly,
  so the export file was being named [object Object].
Updating HTML for script placeholders
Merge pull request #3479 from ErisDS/issue-3079

Complete frontend multi-user features
Changing second half of script placeholders
The page refresh when oauth token has expired was broken.
Ember simple-auth action "sessionInvalidationSucceeded" was overriden to display a meaningless message.
Merge pull request #3425 from jgable/fixImporter

Make importer more robust for tags