* Make ExtUI respect MAXTEMP limits
- Temperatures are now clamped by MAXTEMP limits rather than arbitrary values.
* Speed up USB init, add status
- Speed up USB initialization
- Show status message if init failed
* Enable status messages for EXTENSIBLE_UI
* Adjust max limit to MAX_TEMP - 15
* Misc. tweaks to formatting, const, etc.
* Encapsulate common LCD code in a singleton
* Depend more UBL code on UBL_DEVEL_DEBUGGING
- Since most users don't need the debugging on at all times, this helps reduce the default build size for UBL by over 2K, a little closer to fitting on 128K boards.
