gui, staking: Implement facilities for mandatory sidestakes and sidestake GUI #2907

Job	Run time
Lint	45s
ARM [GOAL install] [buster]	2m 7s
macOS 12 native [GOAL install] [GUI] [no depends]	9m 14s
Win32	2m 42s
Win64	3m 53s
i386 Linux [GOAL install] [focal]	1m 59s
x86_64 Linux [GOAL install] [GUI] [focal] [no depends]	15m 0s
x86_64 Linux [GOAL install] [GUI] [bionic] [no depends]	12m 8s
macOS 10.14 [GOAL deploy] [GUI] [no tests] [focal]	8m 57s
	56m 45s

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