Pass encryption key into CheckDatabaseEncryptionKey

[x2bool]

CheckDatabaseEncryptionKey takes encryption key as a parameter. Database should be encrypted and the key somehow should be stored on computer (OS-specific key storage???).

[worldbeater]

Speaking of local storage, personally I would advise either of these packages: Realm, LiteDB. Perhaps, OS-specific key storage would be more secure (not sure about this), but anyway we need to store preferences, settings (https://github.com/egramtel/egram.tel/issues/22), cache, etc..

[x2bool]

Usually the encryption key is never changed and is stored in some OS keychain

From TdLib Docs

I thinks this means there is some OS-specific keychain where encryption keys are usually stored.

[x2bool]

Yeah we are gonna need some DB. I am up to anything really. I didn't try Realm, but it looks cool.