gui, staking: Implement facilities for mandatory sidestakes and sidestake GUI #2946

Job	Run time
Lint	46s
ARM [GOAL install] [buster]	2m 28s
Win32	2m 28s
Win64	2m 27s
macOS 12 native [GOAL install] [GUI] [no depends]	2m 20s
i386 Linux [GOAL install] [focal]	2m 26s
x86_64 Linux [GOAL install] [GUI] [focal] [no depends]	2m 28s
x86_64 Linux [GOAL install] [GUI] [bionic] [no depends]	2m 27s
macOS 10.14 [GOAL deploy] [GUI] [no tests] [focal]	2m 29s
	20m 19s

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