title: How to add a custom field to a form in IPB
body: <p>Wow, I'm quite amazed that support for Invision Power Board is so lacking (it's paid software!).<br>
  I just can't find the documentation for what I want to do, and I'm talking about stuff I could do in five minutes with any other forum software.</p>
  
  <p>Anyway, the question:
  basically I need to add a custom form field (a select menu) to the 'New Topic' page in my forum. I added a select tag in the <strong>postFormTemplate</strong> template, and I've also created an hook subclassing the <strong>public_forums_post_post</strong> class.
  I'm overriding the <strong>saveForm</strong> function which allows me to save the value of this new field I added. </p>
  
  <p>The problem is: how do I set its initial value? i.e., is there any loadForm function or something like that, which would allow me to load an initial value for the field and then communicate it to the template?
  I hope my question is clear enough. Please ask if you need clarification. </p>