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.

src/config.ts

@@ -6,6 +6,7 @@ const utils = new Utils();
 
 interface SBConfig {
     userID: string,
+    /** Contains unsubmitted segments that the user has created. */
     segmentTimes: SBMap<string, SponsorTime[]>,
     defaultCategory: string,
     whitelistedChannels: string[],