Feature: Add support for ByteArrays/Blobs

[mqus]

This connects the dart type Uint8List to the SQLite data type BLOB and adjusts some tests for that.
Fixes #229.

I'm a newbie to Dart/Flutter so please make sure that I did nothing wrong. I tested it locally but the test didn't get through for an unrelated reason (I assume some race condition?) But I can be wrong.

$ flutter test
00:02 +68 -1: [...]/floor/floor/test/integration/database_test.dart: database tests stream queries insert change find person by id as stream [E]                                                       
  Bad state: Cannot add new events after calling close
  dart:async                                          _BroadcastStreamController.add
  package:floor/src/adapter/query_adapter.dart 68:38  QueryAdapter.queryStream.executeQueryAndNotifyController
  ===== asynchronous gap ===========================
  dart:async                                          _asyncThenWrapperHelper
  package:floor/src/adapter/query_adapter.dart        QueryAdapter.queryStream.executeQueryAndNotifyController
  package:floor/src/adapter/query_adapter.dart 76:55  QueryAdapter.queryStream.<fn>
  ===== asynchronous gap ===========================
  dart:async                                          _ForwardingStream.listen
  package:floor/src/adapter/query_adapter.dart 75:10  QueryAdapter.queryStream
  integration/database.g.dart 167:26                  _$PersonDao.findPersonByIdAsStream
  integration/database_test.dart 274:36               main.<fn>.<fn>.<fn>.<fn>
  
00:03 +77 -1: Some tests failed.  

[vitusortner]

Thanks for your contribution to the library! I've added some remarks to the changes you added.