gui, staking: Implement facilities for mandatory sidestakes and sidestake GUI #2864

Job	Run time
Lint	45s
ARM [GOAL install] [buster]	2m 16s
macOS 12 native [GOAL install] [GUI] [no depends]	6m 5s
Win32	2m 48s
Win64	4m 19s
i386 Linux [GOAL install] [focal]	2m 7s
x86_64 Linux [GOAL install] [GUI] [focal] [no depends]	12m 41s
x86_64 Linux [GOAL install] [GUI] [bionic] [no depends]	12m 23s
macOS 10.14 [GOAL deploy] [GUI] [no tests] [focal]	10m 0s
	53m 24s

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