title: Spring Tool Suite change key binding autocompletion
body: <p>How do I change the keybinding for code autocompletion? <kbd>Ctrl</kbd>+<kbd>Space</kbd> is just horrible. I would like to have <kbd>Alt</kbd>+<kbd>Space</kbd>.
  But under <code>Window-&gt;Preferences-&gt;General-&gt;Keys-&gt;Content Assist</code> I can not choose <kbd>Alt</kbd>+<kbd>Space</kbd>.</p>