Add autobind decorator and fix Android login screen

mobile/src/ui/BoundButton.js

@@ -1,7 +1,7 @@
 import React from 'react'
 import PropTypes from 'prop-types'
 import { View, Text, TouchableHighlight } from 'react-native'
-import { reactAutoBind } from 'auto-bind2'
+import autobind from 'autobind-decorator'
 
 export class BoundButton extends React.Component {
   static propTypes = {
@@ -15,7 +15,6 @@ export class BoundButton extends React.Component {
 
   constructor(props) {
     super(props)
-    reactAutoBind(this)
 
     let { name, binder } = this.props
 
@@ -23,6 +22,7 @@ export class BoundButton extends React.Component {
     this.state = binder.getFieldState(name)
   }
 
+  @autobind
   updateValue(e) {
     this.setState(e.state)
   }