Replace inline styles for logos with css

Also, give .mx_Login_logo a height so that if the image has not loaded yet, it will not change height (thanks @dbkr)

src/components/views/login/VectorLoginHeader.js

@@ -30,7 +30,7 @@ module.exports = React.createClass({
     render: function() {
         return (
             <div className="mx_Login_logo">
-                <img src={this.props.icon || "img/logo.png"} width="195" height="195" alt="Riot"/>
+                <img src={this.props.icon || "img/logo.png"} alt="Riot"/>
             </div>
         );
     }

src/skins/vector/css/matrix-react-sdk/structures/login/_Login.scss

@@ -42,6 +42,11 @@ limitations under the License.
 
 .mx_Login_logo {
     text-align: center;
+    height: 195px;
+}
+
+.mx_Login_logo img {
+    height: 100%
 }
 
 .mx_Login_field {