Linting JSX files (#941)

`.jsx` linting is now in-scope for the `npm run lint` command, and
I linted the base files and some of the viz, there's still quite a bit
of work there, but that's a first pass on it.

caravel/assets/.eslintignore

@@ -1,6 +1,5 @@
 node_modules/*
 vendor/*
 javascripts/dist/*
-visualizations/*
 stylesheets/*
 spec/*

caravel/assets/javascripts/dashboard/Dashboard.jsx

@@ -1,5 +1,5 @@
 const $ = window.$ = require('jquery');
-const jQuery = window.jQuery = $;
+const jQuery = window.jQuery = require('jquery'); // eslint-disable-line
 const px = require('../modules/caravel.js');
 const d3 = require('d3');
 const urlLib = require('url');

caravel/assets/javascripts/dashboard/components/GridLayout.jsx

@@ -90,7 +90,7 @@ class GridLayout extends React.Component {
         rowHeight={100}
         autoSize
         margin={[20, 20]}
-        useCSSTransforms={true}
+        useCSSTransforms
         draggableHandle=".drag"
       >
         {

caravel/assets/javascripts/dashboard/components/SliceAdder.jsx

@@ -3,7 +3,7 @@ import React, { PropTypes } from 'react';
 import update from 'immutability-helper';
 import { BootstrapTable, TableHeaderColumn } from 'react-bootstrap-table';
 import Modal from './Modal.jsx';
-require('../../../node_modules/react-bootstrap-table/css/react-bootstrap-table.css');
+require('react-bootstrap-table/css/react-bootstrap-table.css');
 
 const propTypes = {
   dashboard: PropTypes.object.isRequired,
@@ -129,7 +129,8 @@ class SliceAdder extends React.Component {
 
   render() {
     const hideLoad = this.slicesLoaded || this.errored;
-    const enableAddSlice = this.state.selectionMap && Object.keys(this.state.selectionMap).some(function (key) {
+    let enableAddSlice = this.state.selectionMap && Object.keys(this.state.selectionMap);
+    enableAddSlice = enableAddSlice.some(function (key) {
       return this.state.selectionMap[key];
     }, this);
     const modalContent = (