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
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)
Merge pull request #4367 from jaswilli/issue-4277

Timeout after two seconds on gravatar lookup.
Merge pull request #4371 from jaswilli/fork-timeout

Improve handling of forked processes in tests.
Merge pull request #4372 from jaswilli/deps

Update dependencies.
Editor must be focused before allowing certain keyboard shortcuts.

closes #4253
- checked for the CodeMirror-focused class on the CodeMirror div
- used length to determine whether CodeMirror-focused has been added
- determines whether the editor has been focused on
Update Sass Grunt task output style

No issue

A recent update to NodeSass changed the keyword for output style from `style` to `outputStyle`.
This updates that, thus making the minfied CSS, actually minfied.
Merge pull request #4380 from PaulAdamDavis/sass-compress

Update Sass Grunt task output style
Merge pull request #4155 from jgable/importDuplicates

Remove duplicate posts and tags on import
Merge pull request #4317 from cobbspur/image

Created image helper with absolute url option
Merge pull request #4375 from DaveRobson/#4253

Editor must be focused before allowing certain keyboard shortcuts.