gui, staking: Implement facilities for mandatory sidestakes and sidestake GUI #2862

Job	Run time
macOS 12 native [GOAL install] [GUI] [no depends]	23m 0s
Lint	1m 13s
ARM [GOAL install] [buster]	11m 41s
Win32	13m 44s
Win64	31m 22s
i386 Linux [GOAL install] [focal]	11m 51s
x86_64 Linux [GOAL install] [GUI] [focal] [no depends]	16m 42s
x86_64 Linux [GOAL install] [GUI] [bionic] [no depends]	14m 42s
macOS 10.14 [GOAL deploy] [GUI] [no tests] [focal]	28m 30s
	2h 32m 45s

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