Allow bulk-actions on reports.

There are a number of reports that would benefit from being converted to using reportbuilder, however reportbuilder does not provide a way to facilitate bulk actions - eg select some items in the report using a checkbox selector and delete them/move them/download them etc..

We need the ability to:
1) add a column of checkboxes to the display of the report.
2) have a way to add extra custom actions to a selector allowing for a developer to implement actions like "delete" or "move" or "download zip" that affects the selected items in the report.

This would facilitate bulk actions for the report - eg "delete" all these things, export them, suspend all these users etc.

For example, In a users report, I'd like to be able to select a bunch of users and send them a message.

In a report that shows a list of "files" I'd like to be able to select a bunch and then download them all into a zip file.