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)
Reset/Signin while signed in

no issue
- added redirect and notification to reset route
- added notification to signup route
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
Implementing HTML emails

closes #3082
- no more in-line HTML strings
- adding files for "welcome", "reset password", and "invite user" emails
- added mail.generateContent() to create HTML and plain-text email content
- refactored methods that trigger emails to send both HTML and plain-text emails
Removing "author" role-label

closes #3427
- adding conditional statement to now display users with role "author"
Merge pull request #3421 from morficus/issue-3082

Implementing HTML emails
Merge pull request #3439 from morficus/issue-3427

Removing "author" role-label
Test for invite users error

refs #3433
Add plural handlebars helper

Closes #3414

- Adds a helper which shows a select string deopending on the number of items provided

```
{{plural pagination.total empty='No posts' singular='% post' plural='% posts'}}
```
If `pagination.total` == 0, output 'No Posts'
If `pagination.total` == 1, outputs `1 Post`
If `pagination.total` ==  2 or more, outputs `2 Posts`

Credit to @sebgie for making this work.
Merge pull request #3440 from sebgie/notification-reset-invite

Reset/Signin while signed in
Merge pull request #3415 from PaulAdamDavis/plural-helper

Plural handlebars helper
Improve importer error messaging

closes #3274

- Ensure that validation errors are always handled by moving them into the
  importer
- Ensure that db errors are handled consistently across sqlite and mysql
- Change the errors to be output in a table, with a short failure notification
- Add tests for 003 importing bad files