NoteTile: Also Highlight the title if it matches

Related to #14

lib/widgets/highlighted_text.dart

@@ -0,0 +1,62 @@
+import 'package:flutter/material.dart';
+
+class HighlightedText extends StatelessWidget {
+  final String text;
+  final String highlightText;
+  final String highlightTextLowerCase;
+
+  final TextStyle style;
+  final TextOverflow overflow;
+  final int maxLines;
+
+  HighlightedText({
+    @required this.text,
+    @required this.highlightText,
+    @required this.highlightTextLowerCase,
+    @required this.style,
+    this.overflow,
+    this.maxLines,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    if (highlightText.isEmpty) {
+      return Text(
+        text,
+        maxLines: maxLines - 1,
+        overflow: overflow,
+        style: style,
+      );
+    }
+
+    var i = text.toLowerCase().indexOf(highlightTextLowerCase);
+    if (i == -1) {
+      return Text(
+        text,
+        maxLines: maxLines - 1,
+        overflow: overflow,
+        style: style,
+      );
+    }
+
+    var highlightStyle = style.copyWith(
+      backgroundColor: Theme.of(context).highlightColor,
+    );
+
+    var before = text.substring(0, i);
+    var after = text.substring(i + highlightText.length);
+
+    return RichText(
+      text: TextSpan(
+        children: [
+          TextSpan(text: before, style: style),
+          TextSpan(
+            text: highlightText,
+            style: highlightStyle,
+          ),
+          TextSpan(text: after, style: style),
+        ],
+      ),
+    );
+  }
+}