Fix the shortcut keybindings in editor tab popup menu

Signed-off-by: Umair Khan <omerjerk@gmail.com>

This pull request targets the following issues of the tabs popup menu :

1. The shortcuts worked only until the popup menu was dismissed for the first time. Please refer to this for the reason : http://stackoverflow.com/questions/19862673/jpopup-key-bindings-only-work-1-time
2. The previous tab and next tab options were not working at all as there was no code to handle this.