add checkbox `start` and `finish` on `notifications-stay-visible`.
`notifications-stay-visible` will judged as `false` when given invalid key.
will used as `others` when given invalid `startOrFinish` option.
config UI `notification-stay-visible` change `input` to `select`.
merge upstream/develop
merge upstream/develop again.
merge upstream/develop again.
refactor select element
Merge pull request #209 from senda-akiha/extend-staying-notifications

Extend options for staying notifications