Send through a bot token so messages can be deleted again

Incoming webhooks return no message id, so nothing can be removed later.
Settings now take a bot token plus channel, chat.postMessage records channel
and timestamp on the run, and the history carries a delete button per
message. The webhook stays as a fallback and is marked as not deletable.

messages/en.json

@@ -289,7 +289,13 @@
 			"reportSent": "The digest is out.",
 			"reportEmpty": "Nothing was published in the last seven days, so no message went out.",
 			"reportNoWebhook": "No webhook is stored.",
-			"reportRejected": "Slack rejected the message."
+			"reportRejected": "Slack rejected the message.",
+			"messageDeleted": "The message is deleted in Slack.",
+			"runUnknown": "That run does not exist.",
+			"runNotDeletable": "That run went through the webhook, so there is no message id.",
+			"runNoToken": "Without a bot token nothing can be deleted in Slack.",
+			"runDeleteFailed": "Slack refused the deletion.",
+			"tokenInvalid": "A bot token starts with xoxb or xoxp."
 		},
 		"errors": {
 			"nameRequired": "Enter a name.",
@@ -726,7 +732,8 @@
 				"total": "Entries",
 				"projects": "Projects",
 				"result": "Result",
-				"trigger": "Triggered by"
+				"trigger": "Triggered by",
+				"message": "Message"
 			},
 			"results": {
 				"sent": "Sent",
@@ -736,16 +743,30 @@
 			},
 			"fields": {
 				"webhook": "Incoming webhook",
-				"includeInternal": "Include internal entries"
+				"includeInternal": "Include internal entries",
+				"botToken": "Bot token",
+				"channel": "Channel"
 			},
 			"hints": {
 				"webhook": "From Slack under Incoming Webhooks. The address is bound to one channel.",
 				"includeInternal": "Slack is internal, so this is on by default. Off means customer and public entries only.",
-				"sendNow": "Sends the last seven days into the channel right away."
+				"sendNow": "Sends the last seven days into the channel right away.",
+				"botToken": "From the Slack app under OAuth & Permissions, starts with xoxb. A bot token lets messages be deleted later.",
+				"channel": "Channel name or id, for example logbuch or C01234567."
 			},
 			"errors": {
-				"webhookInvalid": "That does not look like a Slack webhook address."
-			}
+				"webhookInvalid": "That does not look like a Slack webhook address.",
+				"tokenInvalid": "A bot token starts with xoxb or xoxp."
+			},
+			"tokenStored": "Stored, no longer shown.",
+			"replaceToken": "Enter a different token",
+			"messageDelete": "Delete in Slack",
+			"messageDeleting": "Deleting",
+			"messageDeleted": "Deleted",
+			"messageWebhook": "Sent by webhook, cannot be deleted",
+			"pathBot": "Sending through the bot token. Messages can be deleted from here.",
+			"pathWebhook": "Sending through the webhook. Messages cannot be deleted afterwards, that needs a bot token.",
+			"pathNone": "No route stored yet, nothing goes out."
 		}
 	},
 	"filter": {