Add delete post shortcut to content screen

Proposal :: No issue
- cmd/ctrl+backspace deletes a post on the content screen
Fix user settings page for Firefox

References #4050

- Restructures the CSS to work in Firefox - No visual changes, only fixes
Updating dev dependencies

refs #3795

- updates all dev dependencies to their latest version number
- jshint now complains about the Promise global, removed it from predef in
  lieu of a better solution
- changes in should require minor updates to the tests
- tests are passing and all major grunt commands appear to work: clean,
  init, prod, validate and release
Merge pull request #4054 from ErisDS/dev-deps

Updating dev dependencies
Support --reporter and --reporter-output when running tests.

When running any Grunt task that runs tests with Mocha, the two
following command line options are now supported:
- --reporter: allows to specify a reporter, default is 'spec'.
- --reporter-output: allows to specify a file where Mocha's output will
  be stored.

These two command line options make it easier to retrieve and parse test
results when tests are run on a continuous integration platform like
Jenkins.

Fixes #4038.
Merge pull request #4039 from misterdjules/output-tests-results-to-files

Add option to specify reporter and output file via grunt.
Add jscs task to grunt file and clean up files to adhere to jscs rules.

resolves #1920

- updates all files to conform to style settings.
Merge pull request #4001 from hswolff/jscs

Add jscs task to grunt file and clean up files to adhere to jscs rules
Updating express to 4.9.2 & related packages

ref #3795

- express updated to 4.9.2
- express 4.9.0 introduced res.sendStatus() to replace res.status().end()
- we no longer need express-session, connect or cookie-parser
- body-parser, busboy, compression, express-hbs, morgan, all bumped to
  latest versions as well - there doesn't seem to be any breaking changes
Let Ghost serve favicon instead of using dependency

no ref
- Remove static-favicon dependency
- Refactor robots.txt middleware to also serve favicon
- Add ETag
Cleanup reserved words in generateSlug

closes #1889
- Adds a new filter for slugs
- Move slugs to config.slugs
Ignore unknown setting keys on import

fixes #4059
- Ignore NotFound setting keys
Properly handle no posts

fixes #4058
- Set noPosts in setupController
Merge pull request #4061 from ErisDS/issue-3795

Updating express to 4.9.2 & related packages
Mobile view menu for content screen

closes #4031
- Adds css to show back button, edit button in header nav on mobile
Add Tab components

Closes #3937
- Add ghost tab components
- Remove extra container div from Application view
- Move right-outlet viewing logic to application level
- Prepare PSM.hbs for tabbing
Merge pull request #3992 from halfdan/favicon

Let Ghost serve favicon instead of using dependency
Merge pull request #4060 from halfdan/4058-no-posts

Properly handle no posts
Merge pull request #4051 from PaulAdamDavis/fix-user-settings

Fix user settings page for Firefox
Merge pull request #3976 from halfdan/1889-generate-slug

Cleanup reserved words in generateSlug