Remove WidgetCharset class and introduce templated WidgetList class #249

Job	Run time
provide-examples	3s
run-ci (examples/Basic/Basic.ino)	1m 40s
run-ci (examples/Callbacks/Callbacks.ino)	1m 36s
run-ci (examples/CharsetInput/CharsetInput.ino)	1m 50s
run-ci (examples/IntFloatValues/IntFloatValues.ino)	1m 40s
run-ci (examples/ItemBack/ItemBack.ino)	1m 26s
run-ci (examples/List/List.ino)	1m 38s
run-ci (examples/MenuTimeout/MenuTimeout.ino)	1m 24s
run-ci (examples/SubMenu/SubMenu.ino)	1m 36s
run-ci (examples/ViewShifting/ViewShifting.ino)	1m 51s
	14m 44s

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