Remove duplicate posts and tags on import

Issue #806

- Modify sanitize to check for duplicate posts and tags
- Update posts_tags when referencing removed duplicate tags
- Return both data and problems from importData
- Add tests for duplicate posts and tags with fixtures
Created image helper with absolute url option

closes #4231

- Adds {{image}} helper
- Adds image_spec test unit
- Updated {{ghost_head}} to use image helper
Consolidate SimpleAuth.AuthenticatedRouteMixin into AuthenticatedRoute

No issue
Peg node-sass dependency to 1.0.3.

No Issue.
- grunt-sass has node-sass as a dependency (^1.0.0) but the build
  requirements of node-sass version 1.1.0 have changed and will
  fail without a newer version of the gnu compilers.
Merge pull request #4355 from jaswilli/deps-sass

Peg node-sass dependency to 1.0.3.
Added screenshot to readme
Merge pull request #4351 from novaugust/authenticated-route

Consolidate SimpleAuth.AuthenticatedRouteMixin into AuthenticatedRoute
Redirect unauthorized users to signin from debug

Closes #4357
- Adds a call to `this._super()` in DebugRoute#beforeModel to hit the ember simpleauth mixin's beforemodel hook
Merge pull request #4358 from novaugust/unauthed-debug-redirect

Redirect unauthorized users to signin from debug
Update Ember to 1.8.0.

Closes #4316
- Ember@1.8.0.
- Ember-Data@1.0.0-beta.11.
- Change templates to use new Ember.Select syntax and other minor
  cleanup.
- Adjust functional tests.
File structure cleanup
Var cleanup
Better comments

Also introduces a new format of file opening comment, to outline what happens and a contents list.
Merge pull request #4342 from PaulAdamDavis/sass-cleanup

Cleanup modules Sass
Merge pull request #4361 from jaswilli/ember18

Update Ember to 1.8.0.
Handle null/undefined value in test assertion.

No Issue.
- Test is not guaranteed to get a setting that has a "value"
  so we need to handle the case where it's null or undefined.
Merge pull request #4363 from jaswilli/fix-test

Handle null/undefined value in test assertion.
Timeout after two seconds on gravatar lookup.

Refs #4277
- Switch from the built-in http module to request and set
  a timeout of 2 seconds on gravatar lookup requests.
- Move request package from devDependencies to dependencies.
Improve handling of forked processes in tests.

Closes #4277
- Increase the wait time for forked processes to spin up.
- If we give up on waiting for a forked process, send it a
  kill signal so if it comes alive later it doesn't sit in the
  background forever.
- Fail fast if test setup fails instead of waiting for the timeout.
Update dependencies.

No Issue
- bluebird@2.3.10
- bookshelf@0.7.9
- fs-extra@0.12.0
- semver@4.1.0
- grunt-ember-templates@0.4.23 (remove direct dep on ember-template-compiler)
- grunt-sass@0.16.1 (remove direct dep on node-sass)
- remove direct dependency on mocha (only used via grunt-mocha-cli)