add FX_BM26 subprotocol for BM26 P51 and stunt flag for SkyViper Vector #598

Job	Run time
[Test] STM32F103 (128KB)	3m 16s
[Test] STM32F103 (64KB)	3m 15s
[Test] OrangeRX	43s
[Test] STM32F103 (128KB, USB Debug)	3m 40s
[Test] ATmega328p (Optiboot)	3m 12s
[Test] T18 5-in-1 (128KB)	2m 47s
[Test] STM32F103 (128KB, Serial Debug)	3m 33s
[Test] ATmega328p	3m 16s
[Build] ATmega328p	28s
[Build] OrangeRX	24s
[Build] STM32F103 (128KB)	1m 27s
[Build] STM32F103 CC2500 (128KB)	33s
[Build] T-Lite 5-in-1 (128KB)	1m 5s
[Build] STM32F103 (128KB, USB Debug)	18s
[Build] Scripts	11s
[Build] ATmega328p (Optiboot)	34s
[Build] STM32F103 (128KB, Serial Debug)	21s
[Build] STM32F103 5-in-1 (128KB)	58s
[Build] STM32F103 CC2500 (64KB)	32s
[Build] T18 5-in-1 (128KB)	59s
[Deploy] Attach Build Artifacts	5s
[Release] Publish Files to Release	0s
	31m 37s

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