Add Code to process css classes passed to Timebar elements

css classes are processed and handled in the same way that they are when passed to timeline elements.

src/components/Timeline/Grid/index.jsx

@@ -1,10 +1,12 @@
 import React from 'react'
 import PropTypes from 'prop-types'
 
+import createClasses from '../../../utils/classes'
+
 const Grid = ({ time, grid }) => (
   <div className="rt-grid">
-    {grid.map(({ id, start, end }) => (
-      <div key={id} className="rt-grid__cell" style={time.toStyleLeftAndWidth(start, end)} />
+    {grid.map(({ id, start, end, classes }) => (
+      <div key={id} className={createClasses('rt-grid__cell', classes)} style={time.toStyleLeftAndWidth(start, end)} />
     ))}
   </div>
 )

src/components/Timeline/Timebar/Cell.jsx

@@ -1,8 +1,10 @@
 import React from 'react'
 import PropTypes from 'prop-types'
 
-const Cell = ({ time, title, start, end }) => (
-  <div className="rt-timebar__cell" style={time.toStyleLeftAndWidth(start, end)}>
+import createClasses from '../../../utils/classes'
+
+const Cell = ({ time, title, start, end, classes }) => (
+  <div className={createClasses('rt-timebar__cell', classes)} style={time.toStyleLeftAndWidth(start, end)}>
     {title}
   </div>
 )
@@ -14,6 +16,7 @@ Cell.propTypes = {
   title: PropTypes.string.isRequired,
   start: PropTypes.instanceOf(Date).isRequired,
   end: PropTypes.instanceOf(Date).isRequired,
+  classes: PropTypes.arrayOf(PropTypes.string.isRequired),
 }
 
 export default Cell