Clean up segment creation code

Noteworthy changes:
- Adds ability to cancel creating a segment
- Makes segment creation fully the responsibility of the content script, with the popup script buttons simply doing RPC
- Adds types to the Utils.wait function
- Fixes segment timestamps backwards if user marks segment end earlier than the start
- Makes the info menu (in-page popup) workaround clearer and easier to remove in the future.

public/_locales/en/messages.json

@@ -79,6 +79,9 @@
     "sponsorEnd": {
         "message": "Segment Ends Now"
     },
+    "sponsorCancel": {
+        "message": "Cancel Creating Segment"
+    },
     "noVideoID": {
         "message": "No YouTube video found.\nIf this is incorrect, refresh the tab."
     },

public/_locales/pl/messages.json

@@ -79,6 +79,9 @@
     "sponsorEnd": {
         "message": "Koniec segmentu"
     },
+    "sponsorCancel": {
+        "message": "Anuluj tworzenie segmentu"
+    },
     "noVideoID": {
         "message": "Nie znaleziono filmu YouTube.\nJeżeli to błąd, odśwież stronę."
     },