Fixed slashes in From Name setting.

[andrewlimaza]

• BUG FIX: Fixed an issue where the From Name email setting would escape apostrophe's but not remove the slash on the frontend (settings and email received).

Also WPCS was applied to the pmpro_wp_mail_from_name function.

All Submissions:

• Have you followed the Contributing guideline?
• Does your code follow the WordPress' coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

How to test the changes in this Pull Request:

1. Set the from name to something like: PMPro's Test Site and save your settings. You will see it changes PMPro\'s Test Site
2. After pulling this PR, it should set the values back to PMPro's Test Site on the settings page as well as the From name within the email browser.