Customization of Zarafa webapp on Zentyal 3.3

[gr_technologies]

Hi guys! I have a question for you. I've installed Zentyal 3.3 on my server and I have configured Zarafa server and Zarafa WebApp. All works fine. I ask you now if there is a way to customize the WebApp. I don't need to upset it, I only need to add some extra objects, like textfields and comboboxes, for instance, in the "new appointment tab", beneath the 'location' field (see image attached). I need also to store, in the zarafa database, the values that those objects will contain (e.g.: the string inside a textfield or the selected item in a combobox). What I need thus, is to add some new properties to appointments and manage them like the other ones. I've looked for tutorials on the internet but I haven't found anything. I've read the zarafa developers' manual but I don't undestand where to modify the source code to insert my customizations. Any helps? May I try to create a plugin instead of modify the source code? Thank you very much!