Fetch actual raw streamable URLs from various radio-station, video & podcast websites.

Changes for 2.20 - 2023-10-24

• Update default user-agent to: "Mozilla/5.0 (X11; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/115.0"
• StreamFinder::Apple - Handle "embedded" Apple podcasts (https://embed.podcasts.apple.com/). Also fix embedded subsplash.com stream URLs that contain "\u00##" characters and were being trimmed when encountered.
• StreamFinder::Rumble - Convert one of their hosting sites that no longer works (hugh.cdn.rumble.cloud/video) to the standard one that still does (sp.rmbl.ws).
• StreamFinder::Youtube - Try harder to get the first (most recent) video from channel pages (by skipping any "banner" video before it).