Extend Portal component with title, buttons & steps (as per Modal) (#4392)

* Allow Portal to take title & buttons props

* Fix tests

* Portal consistent in screen center

* Allow hiding of Close (e.g. FirstRun usage)

* Set overflow style on body based on open

* Don't lock scroll for child popups (overlaps)

* Override buttons to be white

* Expose ~/ui/Modal/Title as re-usable component

* Use ~/ui/Title to render the Title

* Update tests

* Added a portal example with buttons and steps

* Address PR comments

* Fix AddressSelect with new container withing container

* Move legend to "buttons"

* AddressSelect extra padding

js/src/modals/AddDapps/addDapps.css

@@ -20,7 +20,6 @@
 }
 
 .container {
-  margin-top: 1.5em;
   overflow-y: auto;
 }
 

js/src/modals/AddDapps/addDapps.js

@@ -18,7 +18,7 @@ import { observer } from 'mobx-react';
 import React, { Component, PropTypes } from 'react';
 import { FormattedMessage } from 'react-intl';
 
-import { ContainerTitle, DappCard, Portal, SectionList } from '~/ui';
+import { DappCard, Portal, SectionList } from '~/ui';
 import { CheckIcon } from '~/ui/Icons';
 
 import styles from './addDapps.css';
@@ -41,15 +41,13 @@ export default class AddDapps extends Component {
         className={ styles.modal }
         onClose={ store.closeModal }
         open
+        title={
+          <FormattedMessage
+            id='dapps.add.label'
+            defaultMessage='visible applications'
+          />
+        }
       >
-        <ContainerTitle
-          title={
-            <FormattedMessage
-              id='dapps.add.label'
-              defaultMessage='visible applications'
-            />
-          }
-        />
         <div className={ styles.container }>
           <div className={ styles.warning } />
           {