Give the digest window a way back

Deleting a message that Slack no longer has counts as done, so the window
rewinds instead of staying stuck. A reset button clears the mark by hand,
and the empty-run notice now says since the last dispatch instead of seven
days.

messages/en.json

@@ -287,7 +287,7 @@
 			"typeInUse": "This type is still in use. Clear the active checkbox instead.",
 			"slackSaved": "The Slack settings are saved.",
 			"reportSent": "The digest is out.",
-			"reportEmpty": "Nothing was published in the last seven days, so no message went out.",
+			"reportEmpty": "Nothing appeared since the last digest, so no message went out.",
 			"reportNoWebhook": "No webhook is stored.",
 			"reportRejected": "Slack rejected the message.",
 			"messageDeleted": "The message is deleted in Slack.",
@@ -300,7 +300,8 @@
 			"runNoChannel": "No channel is stored.",
 			"runNotFound": "No matching message found in the channel. Does the bot still need channels:history?",
 			"channelRequired": "A bot token needs a channel, otherwise Logbuch has no target.",
-			"slackSaid": "Slack says: {detail}"
+			"slackSaid": "Slack says: {detail}",
+			"windowReset": "The window is reset. The next digest covers the last seven days again."
 		},
 		"errors": {
 			"nameRequired": "Enter a name.",
@@ -775,7 +776,9 @@
 			"pathNone": "No route stored yet, nothing goes out.",
 			"messageNoToken": "Not deletable without a bot token",
 			"lastSent": "Last sent on {when}. The next digest starts there and only carries what appeared since.",
-			"neverSent": "Nothing sent yet. The first digest covers the last seven days."
+			"neverSent": "Nothing sent yet. The first digest covers the last seven days.",
+			"resetWindow": "Reset the window",
+			"resetting": "Resetting"
 		}
 	},
 	"filter": {