#271 Bulk deletion of per-recipient rules not possible.

[name]

I happened to be editing someones configuration which had a lot per-recipient rules. They were mostly unnecessary and I wanted to delete them.
This turned out to be a real pain - neither were they selectable for bulk deletion nor was I able to delete rules only by using the keyboard without many unnecessary additional movements.
It would be nice if it were possible to select many rules and just delete them in bulk.

[Patrick Brunschwig]

Implemented multi-selection.