Add support for extra mount #709

Job	Run time
Lint	16s
Verify k8s build (ubuntu-latest, 1.19.x)	50s
Build Fyneterm (linux, 1.23.x)	1m 48s
Verify k8s build (macos-latest, 1.19.x)	55s
Build Calculator (linux, 1.23.x)	1m 55s
Build Fyneterm (windows, 1.23.x)	2m 33s
Verify k8s build (windows-latest, 1.19.x)	1m 41s
Test (ubuntu-latest, 1.23.x)	58s
Build Calculator (windows, 1.23.x)	2m 29s
Build Fyneterm (freebsd, 1.23.x)	1m 48s
Test (ubuntu-latest, 1.19.x)	59s
Build Calculator (freebsd, 1.23.x)	1m 46s
Build Fyneterm (android, 1.23.x)	2m 35s
Test (macos-latest, 1.23.x)	47s
Build Fyneterm (linux, 1.19.x)	4m 20s
Build Calculator (android, 1.23.x)	2m 41s
Test (macos-latest, 1.19.x)	1m 9s
Build Fyneterm (windows, 1.19.x)	2m 34s
Build Calculator (web, 1.23.x)	1m 52s
Test (windows-latest, 1.23.x)	2m 23s
Build Calculator (linux, 1.19.x)	1m 42s
Build Fyneterm (freebsd, 1.19.x)	1m 45s
Test (windows-latest, 1.19.x)	2m 32s
Build Calculator (windows, 1.19.x)	2m 22s
Build Fyneterm (android, 1.19.x)	2m 32s
Build Calculator (freebsd, 1.19.x)	3m 54s
Build Calculator (android, 1.19.x)	2m 29s
Build Calculator (web, 1.19.x)	1m 37s
	55m 12s

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