gui, staking: Implement facilities for mandatory sidestakes and sidestake GUI #2883

Job	Run time
Lint	50s
macOS 12 native [GOAL install] [GUI] [no depends]	15m 20s
ARM [GOAL install] [buster]	1m 32s
Win32	1m 48s
Win64	1m 50s
i386 Linux [GOAL install] [focal]	1m 35s
x86_64 Linux [GOAL install] [GUI] [focal] [no depends]	1m 48s
x86_64 Linux [GOAL install] [GUI] [bionic] [no depends]	55s
macOS 10.14 [GOAL deploy] [GUI] [no tests] [focal]	1m 49s
	27m 27s

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