Reset/Signin while signed in

no issue
- added redirect and notification to reset route
- added notification to signup route
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"
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.
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
Uncommenting tests