[firmware][gui] Extended limits fixes, issue #4447 (#4453)
* [firmware][gui] Adjust custom failsafe (and some channel display) ranges for proper extended limits (fixes #4447). This also fixes some display issues in *x64 GUIs when adjusting failsafe settings and cleans up code in those functions.
* [firmware][gui] Fix 480x272 channel output progress bars to show full extended limits; Fix alignment issues on all 212x & 480x gui mixes screens with custom channel names; Streamline some channel outputs display code.
* Fix AVR build.