gui, staking: Implement facilities for mandatory sidestakes and sidestake GUI #2949

Job	Run time
Lint	43s
macOS 12 native [GOAL install] [GUI] [no depends]	16m 16s
ARM [GOAL install] [buster]	8m 22s
Win32	9m 51s
Win64	13m 55s
i386 Linux [GOAL install] [focal]	8m 26s
x86_64 Linux [GOAL install] [GUI] [focal] [no depends]	16m 19s
x86_64 Linux [GOAL install] [GUI] [bionic] [no depends]	15m 48s
macOS 10.14 [GOAL deploy] [GUI] [no tests] [focal]	9m 39s
	1h 39m 19s

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