Display error and prevent new db creation if new db name matches existing db name

ui/src/admin/containers/DatabaseManagerPage.js

@@ -1,6 +1,7 @@
 import React, {PropTypes, Component} from 'react'
 import {connect} from 'react-redux'
 import {bindActionCreators} from 'redux'
+import _ from 'lodash'
 
 import DatabaseManager from 'src/admin/components/DatabaseManager'
 
@@ -57,12 +58,16 @@ class DatabaseManagerPage extends Component {
   }
 
   handleCreateDatabase = database => {
-    const {actions, notify, source} = this.props
+    const {actions, notify, source, databases} = this.props
 
     if (!database.name) {
       return notify('error', 'Database name cannot be blank')
     }
 
+    if (_.findIndex(databases, {name: database.name}, 1)) {
+      return notify('error', 'A database by this name already exists')
+    }
+
     actions.createDatabaseAsync(source.links.databases, database)
   }