Read multiple database on same time

DBFlow Version: 4.1.2

Bug or Feature Request: Feature

Description: Hi, In my condition I have multiple databases as per user accounts. As the app is open a default database is initialized with a user account and user make the local updates and user switch the account and make some changes again in default database that was initialized after switching the account.

Currently, I have a Sync Adapter that sees the local updates in default and sync to the server and now I want to implement the one more functionality. I want to read the local updates from every database and sync on the server on that may be on that time use will be using the app. so there will any database would be initialized according to the user account.

I want to know @agrosner that is there any way that I can read the local updates table from every database like we do in the default database or any other way.

```
RXSQLite.rx(SQLite.select()
.from(UpdatePayload.class))
.queryList().toObservable();
```