Add the ability to delete users
Change warning msg shown when a user is deleted
Add "Last login" filter while deleting users
Remove unused filters from delete users form
Add the ability to schedule auto delete of users by user role

Fix #16
Fix undefined notice while accessing `$this->msg` and `disabled`

If `msg` is not set, then accessing `$this->msg` was generating a
notice. This commit add a `isset()` condition to prevent this notice.
Move menu items under tools menu

Fix #21
Add nonce check while deleting schedules

Fix #24
Update jquery-ui-timepicker addon to v1.4
Change the warning box style to resemble the WP notification box

Fix #23
Edit information about list of available pro addons
Increment version number for v4.0 release
Regenerate pot file for translation