Change refresh token expiry

no issue
- acquiring a new access token using a refresh token sets the
expiration time of the refresh token to now + 24 hrs.
- moved all occurrences of ONE_HOUR, ONE_DAY and ONE_YEAR to
`core/server/utils`
Change casperjs helper used to get RSS page content.

closes #3431
- change feed_test.js to call casperjs getHTML() instead of
  getPageContent(), because the latter now strips markup

Alternative fix would be to use .page.frameContent directly
instead of using a casperjs wrapper.

Change runs cleanly on Travis (old casperjs tag) and locally
in the Ghost-Vagrant setup with both the old casperjs tag
and the current HEAD SHA (29bbd03f7cdc9fc1e70f0fe1400635dd7d3537ad)
Preserve order of tags as entered by the user.

Closes #3133
- Implement an ordered set for the tags property of the tag
  input controller.  Set order is by order added to the post.
Merge pull request #3434 from gleneivey/3431-run-with-latest-casperjs

Change casperjs helper used to get RSS page content.
Merge pull request #3430 from sebgie/refresh-token-expiry

Change refresh token expiry
Merge pull request #3435 from jaswilli/issue-3133

Preserve order of tags as entered by the user.
Error when inviting users

fixes #3433
- passing only the role ID when creating a user
- uncommenting test cases
Merge pull request #3437 from morficus/issue-3433

Error when inviting users