gui, staking: Implement facilities for mandatory sidestakes and sidestake GUI #2919

Job	Run time
macOS 12 native [GOAL install] [GUI] [no depends]	19m 25s
ARM [GOAL install] [buster]	2m 11s
Lint	53s
Win32	2m 52s
Win64	3m 49s
i386 Linux [GOAL install] [focal]	1m 45s
x86_64 Linux [GOAL install] [GUI] [focal] [no depends]	14m 37s
x86_64 Linux [GOAL install] [GUI] [bionic] [no depends]	13m 14s
macOS 10.14 [GOAL deploy] [GUI] [no tests] [focal]	9m 39s
	1h 8m 25s

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