Moodle HQ have recently released a new core plugin for Moodle 3.1, the Recycle Bin. This simply enables Moodle users to recover deleted course components, modules and entire courses if needed.
In addition, the Recycle Bin is flexible, allowing administrators and/or users to determine the length of time items in the bin are stored and deleted.
The recycle bin is available by default in all courses and categories, the link in the administration block is only visible when something has been deleted.
As an administrator you can decide to turn off the recycle bin and modify the settings (such as length of time an item will remain in the recycle bin) through Site administration > Plugins > Admin tools > Recycle bin.
You can find out more about the plugin at https://moodle.org/plugins/local_recyclebin.