Swapped Flex to homegrown component

No more element prop warnings!

frontend/scenes/Document/Document.js

@@ -4,7 +4,7 @@ import get from 'lodash/get';
 import styled from 'styled-components';
 import { observer, inject } from 'mobx-react';
 import { withRouter, Prompt } from 'react-router';
-import { Flex } from 'reflexbox';
+import Flex from 'components/Flex';
 
 import Document from 'models/Document';
 import UiStore from 'stores/UiStore';

frontend/scenes/Home/Home.js

@@ -2,7 +2,7 @@
 import React from 'react';
 import { observer, inject } from 'mobx-react';
 import { Redirect } from 'react-router';
-import { Flex } from 'reflexbox';
+import Flex from 'components/Flex';
 import styled from 'styled-components';
 
 import AuthStore from 'stores/AuthStore';

frontend/scenes/Search/Search.js

@@ -3,7 +3,7 @@ import React from 'react';
 import ReactDOM from 'react-dom';
 import { observer } from 'mobx-react';
 import _ from 'lodash';
-import { Flex } from 'reflexbox';
+import Flex from 'components/Flex';
 import { withRouter } from 'react-router';
 import { searchUrl } from 'utils/routeHelpers';
 import styled from 'styled-components';

frontend/scenes/Search/components/SearchField/SearchField.js

@@ -1,6 +1,6 @@
 // @flow
 import React, { Component } from 'react';
-import { Flex } from 'reflexbox';
+import Flex from 'components/Flex';
 import styled from 'styled-components';
 import searchImg from 'assets/icons/search.svg';
 

frontend/scenes/Settings/Settings.js

@@ -1,7 +1,7 @@
 // @flow
 import React from 'react';
 import { observer } from 'mobx-react';
-import { Flex } from 'reflexbox';
+import Flex from 'components/Flex';
 
 import ApiKeyRow from './components/ApiKeyRow';
 import styles from './Settings.scss';