View name override

[rkistner]

Supports:

1. Overriding the view name for tables: Table(..., viewName: 'local_table').
2. Updating the schema after the database has already been opened (but before connecting sync): await db.updateSchema(schema)

This allows having separate tables for a synced mode and a local-only mode, and moving data between the two - see the tests. The use case is a user first using the app completely offline (without registering an account), then potentially at a later stage connecting an account and syncing data, without the upload queue continuously growing in size before that.

Additional changes:

1. Validate schema definitions for duplicates and invalid names.
2. Support preserving local-only tables when clearing database: await db.disconnectAndClear(clearLocal: false).

[kobiebotha]

🚀