Suggestions for new version

[Samfun75]

• Expose network.defaultUserAgent for extensions to use when user changes user-agent
• Allow extensions to provide skip times along side aniskip, there are bigger databases of skip times than aniskip (zoro & 9anime)
• Allow extensions to provide mal/anilist/kitsu id for auto tracking purposes (zoro & pahe)
• A none episode identifier for episodes so that for extensions that provided OVA and Movies with episodes can correctly report number of episodes, might be useful for trackers too
• Expose a function to retrieve episodes so that extensions can decide to update the whole list of episodes or for supported only the last season when refreshing (there can also be a force refresh option from ellipses menu to force update all episode list, like how it's done normally now, it could be a flag passed to the fetchepisodelist that extensions can check)