OSX shortcut fix.

closes #2573
- separate different shortcuts by OS detection in markdownEditor.js
Merge pull request #2574 from LazyChild/issue-2573

OSX shortcut fix.
Added email sending endpoint to the API.
closes #2550

- Added new API module named 'mail'
- Added routes for the mail endpoint
- Added 'send a test email' button to the debug settigns page
- Added handler to this button which sends and AJAX request to the mail API endpoint