luigetter: factor out base class of LuiGetter

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
luigen: rename, add LuiSetter

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
lui: convert task-mode and lube to luigen setters

Signed-off-by: Jeff Epler <jepler@unpythonic.net>