Use new method of getting team icon

This was necessary because the team token may not be known when registering, but domain is. Storing the icon under the "common" directory is the chosen solution to this.

src/components/structures/login/Registration.js

@@ -426,7 +426,12 @@ module.exports = React.createClass({
         return (
             <div className="mx_Login">
                 <div className="mx_Login_box">
-                    <LoginHeader icon={this.state.teamSelected ? this.state.teamSelected.icon : null}/>
+                    <LoginHeader
+                        icon={this.state.teamSelected ?
+                            "https://riot.im/rts/static/common/" +
+                            this.state.teamSelected.domain + "/icon.png" :
+                            null}
+                    />
                     {this._getRegisterContentJsx()}
                     <LoginFooter />
                 </div>