Merge branch 'release/v2.7.6' into develop
Fixing a bug with sub editing.
Adding notification class.
Adding a notifications table.
Adding notification table output.
Adding functions for interacting with notifications.
Adding table for notifications.
Added table layout for notifications settings
Added notification activation code.
Merge branch 'feature/notifications' of https://github.com/wpninjas/ninja-forms into feature/notifications

Conflicts:
	classes/notifications.php
Fixing merge conflicts.
Continuing to work on the notification table.
Continuing to work on the notification table.
Adding a registration class for fields, notifications, and sidebars.
Creating a notification types class to instantiate all of our registered notification types.
Adding specific notification types.
Creating some initial notification types.
Fixes #269.
Fixed an invalid argument error when viewing a the submissions table

Warning: Invalid argument supplied for foreach() in (...)/wp-content/plugins/ninja-forms/classes/subs-cpt.php on line 274
Fixed a bug with some servers caused by calling the set_time_limit() function.