[Feature] Add `compact()` to FlashStore@0.18 with Medea DB

[huan]

See: wechaty/wechaty-puppet-padplus#155

API reference of Medea: https://github.com/medea/medea/blob/master/README.md#dbcompactcallback

[huan]

MedaeDB has been deprecated.