Keep shown items in favorite sessions

[hironytic]

Issue

• related #642

Overview (Required)

• Leave session items which have ever been shown in favorites

Links

• None

Screenshot

• None

[takahirom]

I think this is not best implementation （I want to use snackbar button） But this is usefull. Let me merge

[hironytic]

Thanks. OK🙆 I cannot implement snackbar approach, to make it possible to undo, because of luck of my skill. Feel free to revert my code when snackbar implementation has done🙂