Add GroupAvatar to handle fallback images etc.

And a few misc tidyups

src/components/views/avatars/GroupAvatar.js

@@ -0,0 +1,62 @@
+/*
+Copyright 2017 Vector Creations Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import React from 'react';
+import PropTypes from 'prop-types';
+import sdk from '../../../index';
+import MatrixClientPeg from '../../../MatrixClientPeg';
+
+export default React.createClass({
+    displayName: 'GroupAvatar',
+
+    propTypes: {
+        groupId: PropTypes.string,
+        groupAvatarUrl: PropTypes.string,
+        width: PropTypes.number,
+        height: PropTypes.number,
+        resizeMethod: PropTypes.string,
+    },
+
+    getDefaultProps: function() {
+        return {
+            width: 36,
+            height: 36,
+            resizeMethod: 'crop',
+        };
+    },
+
+    getGroupAvatarUrl: function(props) {
+        return MatrixClientPeg.get().mxcUrlToHttp(
+            this.props.groupAvatarUrl,
+            this.props.width,
+            this.props.height,
+            this.props.resizeMethod,
+        );
+    },
+
+    render: function() {
+        const BaseAvatar = sdk.getComponent("avatars.BaseAvatar");
+
+        return (
+            <BaseAvatar
+                name={this.props.groupId[1]}
+                idName={this.props.groupId}
+                url={this.getGroupAvatarUrl()}
+                {...this.props}
+            />
+        );
+    }
+});