Add delete post shortcut to content screen

Proposal :: No issue
- cmd/ctrl+backspace deletes a post on the content screen
Ignore unknown setting keys on import

fixes #4059
- Ignore NotFound setting keys
Mobile view menu for content screen

closes #4031
- Adds css to show back button, edit button in header nav on mobile
Prevent transition to signup on invalid invitation

Refs #3876
- Prevent signup page from flashing when an invalid invitation
  token is used.
- Clear sensitive information from signup controller.
- Make isInvitation API behavior consistent with other auth
  related APIs.
GhostGFM honours escaped tildes

fixes #2703

- adds an extra rule to remove the slash if a tilde is escaped as showdown
  won't do this.
Have /ghost use its own express instance

closes #1961
- Refactor admin to use its own express instance
- Refactor middlewares to work with /ghost mounted admin express instance
Merge pull request #4045 from halfdan/4031-mobile-content

Mobile view menu for content screen
Merge pull request #4056 from halfdan/1961-wuaeh

Have /ghost use its own express instance
Adds grunt lint task for code style checking

no issue

- convenience function runs both jshint and jscs
Delay updateCheck to +24h on error

fixes #4036
- delay update check by 24h when an error happens
- set connection timeout to 10 seconds
Merge pull request #4048 from novaugust/delete-post-shortcut

[Feature request] Add delete post shortcut to content screen
Merge pull request #4040 from halfdan/4036-update-check

Delay updateCheck to +24h on error
Merge pull request #4062 from halfdan/4059-skip-not-found

Ignore unknown setting keys on import
Merge pull request #4063 from ErisDS/issue-2703

GhostGFM honours escaped tildes
Merge pull request #4070 from ErisDS/grunt-lint

Adds grunt lint task for code style checking
Merge pull request #4065 from jaswilli/transition

Prevent transition to signup on invalid invitation
Implements spin-button

closes #3928
- Adds gh-spin-button component
- CSS for spinning button