Fix main header being redrawn every 100ms

ts/components/MainHeader.tsx

@@ -88,7 +88,9 @@ export class MainHeader extends React.Component<Props, any> {
 
     setInterval(() => {
       const clipboardText = clipboard.readText();
+      if (this.state.clipboardText !== clipboardText) {
         this.setState({ clipboardText });
+      }
     }, 100);
   }