Added optional clear button

Author: blackjk3

.gitignore

@@ -8,4 +8,5 @@
 /build
 
 .DS_Store
+npm-debug.log
 /node_modules/*

app.js

@@ -2,6 +2,6 @@ import React from "react";
 import SignaturePad from "./src/index";
 
 React.render(
-  <SignaturePad />,
+  <SignaturePad clearButton="true" />,
   document.body
 )

src/index.js

@@ -295,6 +295,11 @@ export default class SignaturePad extends React.Component {
         <div className="m-signature-pad--body">
           <canvas ref="cv"></canvas>
         </div>
+        { this.props.clearButton &&
+          <div className="m-signature-pad--footer">
+            <button className="btn btn-default button clear" onClick={this.clear.bind(this)}>Clear</button>
+          </div>
+        }
       </div>
     );
   }