Ensure cookies are only ever set for admin

fixes #1901

- Adds a trailing slash to the cookie path
- Resolves random log-outs
- Adds a test which proves the case
Merge pull request #1910 from ErisDS/issue-1901

Ensure cookies are only ever set for admin
Minor fixes to asset helper and tests

no issue

- asset helper ignores it if theme devs specify the asset dir
- asset helper strips leading slashes
- static asset tests were wrong
Error message updates

no issue

- couple of tweaks to the messaging of non-fatal errors that can be output when running Ghost
Updating to latest Casper
Bump version for pre-release 3
2013 => 2014
Merge pull request #1917 from JohnONolan/copyright

2013 => 2014
Updating to latest Casper
Publish date and time display fix

no issue

- add @ symbol to ensure date and time are clear
Merge pull request #1919 from ErisDS/date-display

Publish date and time display fix
Version bump for 0.4 release