Add entry delete buttons

Adds entry delete buttons as requested in #819 (closed). Entries can be removed either from the table on the upload overview page or from the entry overview page. A new endpoint was created: uploads/{upload_id}/action/delete-entry-files, which allows the deletion of entry files based on a query (restricted to a single upload). When clicking the delete buttons, a dialog is opened, asking the user to confirm, and to specify if we should delete only the mainfiles or the mainfiles + their folders.