BETA release, proceed with caution ;)

What's Changed

• Bugfix for brightness factor upon save: fixes #4824 by @DedeHai in #4827
• 0.15 - updated AsyncWebServer and AsyncTCP by @willmmiles in #4834
• (0.15.2 backport): Make version information consistent across update interfaces by @Arcitec in #4849
• (0.15.2 backport) Fix broken Sync button after 0.15 refactor by @Arcitec in #4845
• fix ancient UI bug that hides the speed slider in percent FX 0.15 edition by @DedeHai in #4914
• bugfix: do not reset segments if unchanged by @DedeHai in #4969
• Bugfix for FX: Tri Fade by @blazoncek in #4918
• (0.15) RMT High-priority Interrupt driver backport by @willmmiles in #4980
• fix buffer size calculation for ESP8266 (0.15 edition) by @DedeHai in #4951
• 0.15 version of OTA validation by @willmmiles in #4999
• 0.15 - Fix bin file output names by @willmmiles in #5034

Full Changelog: v0.15.1...0.15.2-beta1