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