Add bulk delete for Activities page

[afadil]

Add a bulk delete option on the Activities page to quickly remove many activities at once. Users can select multiple activities and delete them at once. Confirm before deletion. The column header has a checkbox to select all filtered activities.

[avishai]

There should also be a way to force recalculate everything after a bulk delete or deleting an account. I've tried to start from scratch, but there is a lag with totals and positions appearing from deleted accounts and activities.