Add recording selector

As a proof of concept some widgets were seperated. The home screen now
links to this instead of the recording editor.

lib/widgets/performance_row.dart

@@ -0,0 +1,42 @@
+import 'package:flutter/material.dart';
+
+import '../backend.dart';
+import '../database.dart';
+
+import 'person_text.dart';
+import 'ensemble_text.dart';
+
+class PerformanceRow extends StatelessWidget {
+  final Performance performance;
+
+  PerformanceRow(this.performance);
+
+  @override
+  Widget build(BuildContext context) {
+    final backend = Backend.of(context);
+
+    return Row(
+      children: <Widget>[
+        if (performance.person != null)
+          PersonText(performance.person)
+        else if (performance.ensemble != null)
+          EnsembleText(performance.ensemble),
+        if (performance.role != null) ...[
+          SizedBox(
+            width: 4.0,
+          ),
+          StreamBuilder<Instrument>(
+            stream: backend.db.instrumentById(performance.role).watchSingle(),
+            builder: (context, snapshot) {
+              if (snapshot.hasData) {
+                return Text('(${snapshot.data.name})');
+              } else {
+                return Container();
+              }
+            },
+          ),
+        ],
+      ],
+    );
+  }
+}