Implement 'clear' flag in ISyncProtocol

[dfahlander]

The applyRemoteChanges() has a not-implemented 'clear' flag that should be implemented for the cases when a client has been offline for a very long time so that the server no more has the old revision saved, that the client refers to.

See nponiros/sync_server#5

[cbrachem]

I don't know much about the inner workings of Dexie or IndexedDB yet, but let me state the idea of replacing the return value of applyRemoteChanges(), shown here:

return (partial ? saveToUncommittedChanges(remoteChanges, remoteRevision) : finallyCommitAllChanges(remoteChanges, remoteRevision))
    .catch(function (error) {
      abortTheProvider(error);
      return Promise.reject(error);
    });

with something like this:

return (clear ? Promise.all(db.tables.map(table => table.clear())) : Promise.resolve())
    .then(() => partial ? saveToUncommittedChanges(remoteChanges, remoteRevision) : finallyCommitAllChanges(remoteChanges, remoteRevision))
    .catch(function (error) {
      abortTheProvider(error);
      return Promise.reject(error);
    });

What would be wrong with that?