Enhancement: Batch actions for accepting and declining shares

We've added batch actions for accepting and declining multiple selected incoming shares at once.

https://github.com/owncloud/web/issues/5204
https://github.com/owncloud/web/pull/5374
https://github.com/owncloud/web/issues/2513
https://github.com/owncloud/web/issues/3101
https://github.com/owncloud/web/issues/5435
