gui, staking: Implement facilities for mandatory sidestakes and sidestake GUI #2953

Job	Run time
macOS 12 native [GOAL install] [GUI] [no depends]	13m 34s
ARM [GOAL install] [buster]	2m 19s
Lint	52s
Win32	2m 42s
Win64	3m 58s
i386 Linux [GOAL install] [focal]	1m 50s
x86_64 Linux [GOAL install] [GUI] [focal] [no depends]	15m 19s
x86_64 Linux [GOAL install] [GUI] [bionic] [no depends]	14m 42s
macOS 10.14 [GOAL deploy] [GUI] [no tests] [focal]	9m 28s
	1h 4m 44s

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