PLT-2643 Fixed asynchronous autocomplete incorrectly replacing text (#3167)

* Allowed different suggestions to match different text. Added a Suggestion base component. Improved text replacement used when filling in suggestions

* Fixed formatting

webapp/tests/suggestion_box.test.jsx

@@ -0,0 +1,20 @@
+// Copyright (c) 2016 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+import assert from 'assert';
+
+import SuggestionBox from 'components/suggestion/suggestion_box.jsx';
+
+describe('SuggestionBox', function() {
+    it('findOverlap', function(done) {
+        assert.equal(SuggestionBox.findOverlap('', 'blue'), '');
+        assert.equal(SuggestionBox.findOverlap('red', ''), '');
+        assert.equal(SuggestionBox.findOverlap('red', 'blue'), '');
+        assert.equal(SuggestionBox.findOverlap('red', 'dog'), 'd');
+        assert.equal(SuggestionBox.findOverlap('red', 'education'), 'ed');
+        assert.equal(SuggestionBox.findOverlap('red', 'reduce'), 'red');
+        assert.equal(SuggestionBox.findOverlap('black', 'ack'), 'ack');
+
+        done();
+    });
+});